test(runtime): validate native systems configuration matrix

[PhilipJohnBasile]

Temporary validation PR for the exact candidate intended for upstream PR youssofal#336.

Matrix

• Linux pure-Python system tests on Python 3.11, 3.12, 3.13, and 3.14
• isolated process profiles: default-off, expert-only, unified-memory-only, and combined-memory
• macOS 14 ARM64 runtime integration including the dashboard endpoint contract
• JUnit artifacts for every matrix cell

Added cross-system coverage

• feature activation and default-off fast path
• every safe-point blocker and fail-closed mutation boundary
• environment clamping and OTLP endpoint normalization
• all-enabled memory, OTLP, policy, and replay interaction
• privacy-default telemetry behavior
• concurrent first-use idempotency and namespaced runtime state

This PR will be closed after the exact head is validated; the single test commit will then be appended to upstream PR youssofal#336.

[PhilipJohnBasile]

Exact validation head 53ba0cc1bc96b135da32fba25615dfff96b81bf6 passed all fork-side gates:

• build — PASS
• ci — PASS
• hygiene — PASS
• native-adaptive — PASS
• all 9 matrix cells — PASS
• Python 3.11, 3.12, 3.13, and 3.14 pure-system suites — 143 tests each
• macOS 14 ARM64 integration — 185 tests
• isolated default-off, expert-only, unified-memory-only, and combined-memory process profiles — PASS

This temporary validation PR is being closed. Its single test/CI commit is being appended to upstream MTPLX PR youssofal#336.