feat(Init): Initial upload of array + interoperability package

.github/CODEOWNERS

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+* @Simpag @nicola-bastianello

.gitignore

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+**/__pycache__
+**/build
+*.egg-info
+*.so
+.DS_Store
+.mypy_cache
+.tox
+.vscode
+dist
+pyrightconfig.json
+.claude
+*.py[codz]
+*$py.class

benchmarks/bench_array.py

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+"""
+Microbenchmark: ``decent_array.Array`` operator overhead vs native frameworks.
+
+Measures the wrapper cost added by routing operators through ``Array.__add__``,
+``Array.__neg__`` etc. against calling the framework's native operators
+directly. Iterates over every framework whose package is importable; missing
+optional dependencies are skipped silently.
+
+The overhead column is ``wrapped / native`` runtime — values close to 1.0x mean
+the wrapper is essentially free. Large values at small sizes are expected
+(operator dispatch dominates) and should converge toward 1.0x as elementwise
+work grows.
+
+Run with::
+
+    python benchmarks/bench_array.py
+"""
+
+from __future__ import annotations
+
+from bench_common import (
+    SIZES,
+    BackendCase,
+    activate_backend,
+    discover_backends,
+    fmt_row,
+    parse_backends_arg,
+    print_preamble,
+    print_size_header,
+    time_us_safe,
+)
+
+from decent_array import Array
+
+
+def _bench_case(case: BackendCase) -> None:
+    activate_backend(case.name)
+    print(f"## {case.name}\n")
+    for n in SIZES:
+        a = case.make(n)
+        b = case.make(n)
+        d_a, d_b = Array(a), Array(b)
+
+        print_size_header(n)
+        rows = (
+            ("add", lambda a=a, b=b: a + b, lambda d_a=d_a, d_b=d_b: d_a + d_b),
+            ("sub", lambda a=a, b=b: a - b, lambda d_a=d_a, d_b=d_b: d_a - d_b),
+            ("mul", lambda a=a, b=b: a * b, lambda d_a=d_a, d_b=d_b: d_a * d_b),
+            ("div", lambda a=a, b=b: a / b, lambda d_a=d_a, d_b=d_b: d_a / d_b),
+            ("neg", lambda a=a: -a, lambda d_a=d_a: -d_a),
+            ("abs", lambda a=a: abs(a), lambda d_a=d_a: abs(d_a)),
+            ("pow", lambda a=a: a ** 2.0, lambda d_a=d_a: d_a ** 2.0),
+        )
+        for op, native_fn, wrapped_fn in rows:
+            n_us = time_us_safe(case, native_fn)
+            w_us = time_us_safe(case, wrapped_fn)
+            print(fmt_row(op, n_us, w_us))
+        print()
+    print()
+
+
+def main() -> None:
+    print_preamble("Array operator overhead vs native frameworks")
+    cases = discover_backends(only=parse_backends_arg())
+    print(f"available backends: {', '.join(c.name for c in cases)}\n")
+    for case in cases:
+        _bench_case(case)
+
+
+if __name__ == "__main__":
+    main()

benchmarks/bench_common.py

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+"""
+Shared helpers for ``bench_array.py`` and ``bench_iop.py``.
+
+Three concerns live here so the benchmarks stay focused on the comparison logic:
+
+* :func:`discover_backends` returns the subset of frameworks whose package is
+  importable; backends with a missing optional dependency are skipped silently.
+* :func:`is_compiled` / :func:`print_preamble` report whether the user is
+  running against a mypyc-compiled build of ``decent_array`` or the pure-Python
+  source — this materially changes overhead numbers, so the result is printed
+  at the top of every run.
+* :func:`time_us` / :func:`time_us_safe` wrap :mod:`timeit` to take the
+  ``min`` of several auto-ranged repeats. ``min`` is the canonical choice: it
+  reports the lower bound of the machine's per-call cost and is the metric
+  least sensitive to background activity. A warmup call precedes timing so
+  JIT-style backends (JAX) don't skew the first iteration.
+"""
+
+from __future__ import annotations
+
+import importlib
+import timeit
+from collections.abc import Callable
+from dataclasses import dataclass
+from typing import Any
+
+SIZES: tuple[int, ...] = (10, 100, 1_000, 10_000)
+REPEATS: int = 7
+
+
+def _no_sync(_value: Any) -> None:  # noqa: ANN401
+    """No-op sync used for synchronous backends (numpy, torch CPU, tf eager CPU)."""
+
+
+def _sync_jax(value: Any) -> None:  # noqa: ANN401
+    """Block until a JAX DeviceArray is materialized, unwrapping ``Array`` if needed."""
+    # Imported lazily so the module can load even when decent_array isn't yet importable.
+    from decent_array import Array  # noqa: PLC0415
+
+    raw = value.value if isinstance(value, Array) else value
+    raw.block_until_ready()
+
+
+@dataclass(slots=True)
+class BackendCase:
+    """A discovered backend plus the helpers needed to drive it in a benchmark."""
+
+    name: str
+    make: Callable[[int], Any]
+    sync: Callable[[Any], None]
+
+
+def activate_backend(name: str) -> None:
+    """Activate ``name`` as the live backend, resetting any previously active one.
+
+    ``decent_array`` enforces a single-active-backend invariant per execution context;
+    swapping between frameworks within one process requires resetting first.
+    """
+    from decent_array.interoperability._backend_manager import reset_backends, set_backend  # noqa: PLC0415
+
+    reset_backends()
+    set_backend(name)
+
+
+def discover_backends(only: list[str] | None = None) -> list[BackendCase]:
+    """Return one :class:`BackendCase` per importable framework, in a stable order.
+
+    Args:
+        only: Optional allowlist of backend names. When provided, frameworks not in the
+            list are skipped entirely (their packages aren't even imported), and any
+            requested name that isn't a known backend raises :class:`ValueError`.
+
+    """
+    import numpy as np  # always available — hard dependency  # noqa: PLC0415
+
+    known = {"numpy", "pytorch", "jax", "tensorflow"}
+    if only is not None:
+        unknown = set(only) - known
+        if unknown:
+            raise ValueError(f"unknown backend(s): {sorted(unknown)}; known: {sorted(known)}")
+        wanted = set(only)
+    else:
+        wanted = known
+
+    cases: list[BackendCase] = []
+
+    if "numpy" in wanted:
+        cases.append(BackendCase("numpy", lambda n: np.random.rand(n), _no_sync))
+
+    if "pytorch" in wanted:
+        try:
+            import torch  # noqa: PLC0415
+        except ImportError:
+            pass
+        else:
+            cases.append(BackendCase("pytorch", lambda n: torch.from_numpy(np.random.rand(n)), _no_sync))
+
+    if "jax" in wanted:
+        try:
+            import jax.numpy as jnp  # noqa: PLC0415
+        except ImportError:
+            pass
+        else:
+            cases.append(BackendCase("jax", lambda n: jnp.asarray(np.random.rand(n)), _sync_jax))
+
+    if "tensorflow" in wanted:
+        try:
+            import tensorflow as tf  # noqa: PLC0415
+        except ImportError:
+            pass
+        else:
+            cases.append(BackendCase("tensorflow", lambda n: tf.constant(np.random.rand(n)), _no_sync))
+
+    return cases
+
+
+def parse_backends_arg() -> list[str] | None:
+    """Parse the shared ``--backends`` CLI flag; returns ``None`` if not given."""
+    import argparse  # noqa: PLC0415
+
+    parser = argparse.ArgumentParser(add_help=True)
+    parser.add_argument(
+        "--backends",
+        type=str,
+        default=None,
+        help="comma-separated allowlist of backends (numpy,pytorch,jax,tensorflow); default = all available",
+    )
+    args = parser.parse_args()
+    if args.backends is None:
+        return None
+    return [b.strip() for b in args.backends.split(",") if b.strip()]
+
+
+def is_compiled() -> tuple[bool, str]:
+    """Return ``(True, path)`` if the Array module loaded from a ``.so``/``.pyd``, else ``(False, .py path)``."""
+    module = importlib.import_module("decent_array._array")
+    path = module.__file__ or "<unknown>"
+    return path.endswith((".so", ".pyd")), path
+
+
+def print_preamble(title: str) -> None:
+    compiled, path = is_compiled()
+    print(f"# {title}\n")
+    print(f"decent_array compiled: {'yes' if compiled else 'no'}")
+    print(f"  Array loaded from: {path}")
+    print(f"  timing: min over {REPEATS} repeats, iterations per repeat auto-tuned to ~0.2s\n")
+
+
+def time_us(case: BackendCase, fn: Callable[[], Any]) -> float:
+    """Per-call runtime in µs; min over :data:`REPEATS` measurements with autoranged N."""
+
+    def runner() -> None:
+        case.sync(fn())
+
+    runner()  # warmup — material for JAX's first-call compilation
+    timer = timeit.Timer(runner)
+    n, _ = timer.autorange()
+    times = timer.repeat(repeat=REPEATS, number=n)
+    return (min(times) / n) * 1e6
+
+
+def time_us_safe(case: BackendCase, fn: Callable[[], Any]) -> float | None:
+    """Like :func:`time_us` but returns ``None`` if ``fn`` raises (e.g. TF 1D matmul)."""
+    try:
+        return time_us(case, fn)
+    except Exception:  # noqa: BLE001
+        return None
+
+
+def fmt_row(op: str, native_us: float | None, wrapped_us: float | None) -> str:
+    if native_us is None or wrapped_us is None:
+        return f"   {op:<8}  {'n/a':>13}  {'n/a':>13}   {'n/a':>8}"
+    ratio = wrapped_us / native_us if native_us > 0 else float("inf")
+    return f"   {op:<8}  {native_us:>10.3f} µs  {wrapped_us:>10.3f} µs   {ratio:>6.2f}x"
+
+
+def print_size_header(n: int) -> None:
+    print(f"size = {n:_}")
+    print(f"   {'op':<8}  {'native':>13}  {'wrapped':>13}   {'overhead':>8}")