test: native config collision matrix for all 4 tools

[0xjgv]

Summary

• Parametrised tool_config_source matrix: all 4 tools (ruff, basedpyright, coverage, import-linter) report bundled in bare project, project: when their [tool.*] section is present
• 12-pair cross-tool isolation test: each [tool.<X>] section must never suppress bundled config for any other tool
• .importlinter sidecar detection test for arch task (previously untested path; [tool.importlinter] was covered, sidecar was not)
• Task-level cross-tool FP spot-checks in lint, typecheck, coverage, format, format-check verifying suppression decision wires through to actual CLI flags
• Hoist _BARE constant above all callers in test_defaults_path.py; eliminate duplicate definition

Test plan

• uv run pytest -q tests/test_defaults_path.py tests/tasks/test_lint.py tests/tasks/test_format.py tests/tasks/test_format_check.py tests/tasks/test_typecheck.py tests/tasks/test_coverage.py tests/tasks/test_arch.py — 82 pass (up from 50 baseline)
• uv run interlocks check --changed — clean on the 7 files in this commit

[gemini-code-assist]

Code Review

This pull request introduces a comprehensive suite of tests to ensure cross-tool isolation and correct configuration handling across various tasks like linting, formatting, type-checking, and coverage. It specifically verifies that the presence of configuration for one tool does not suppress the bundled defaults for others and validates the propagation of tool version pins. A syntax error was identified in a test setup where a TOML string value was missing quotes, which would lead to a decoding error.

[gemini-code-assist]

The root_package value in the pyproject.toml string is missing quotes. Since pyproject.toml is a TOML file, string values must be quoted to be valid. This will cause a tomllib.TOMLDecodeError when the configuration is loaded during the test execution.

Suggested change

	root_package = archpin
	root_package = "archpin"