ci: skip a Python member's quality matrix when a lock change doesn't touch it

[dominickdupuy]

Why

Every Python member's paths: filter lists uv.lock and pyproject.toml, because the workspace shares one lockfile. So any dependency change fans out to every member. On #16, a data-ngin dependency change queued algosystem's six-job matrix: Python 3.11 and 3.13 on Ubuntu, macOS and Windows.

What

_quality-python.yml gains a detect job, needs quality?, which runs platform/ci/quality_needed.py. The quality matrix runs only when it says run=true:

Changed (within the caller's paths)	Result
any file other than uv.lock (member code, workspace deps it lists, root pyproject.toml, CI files)	run
only uv.lock	run only if the member's resolved closure differs between base and head
nothing	skip

The closure is every package reachable from the member in uv.lock, across all extras and groups (CI installs them all), plus the workspace root's dev group (pytest, ruff, mypy). Each entry is compared in full: version, source and hashes.

It fails open. With no base commit (new branch, dispatch), an unreadable lock, or a caller with no pull_request.paths (the deploy and publish workflows), the matrix runs. Skipped matrices still report success, so each member's gate check stays green.

Checked on real history

Change	algosystem	research-core	algoterminal	research-api	data-ngin
Airflow 3 commit (uv.lock + data-ngin files)	run (sqlalchemy, greenlet moved)	skip	skip	skip	run
#16 (also touched root pyproject.toml)	run	run	—	run	run

Root pyproject.toml changes still run everything, because it holds the shared ruff, mypy and pytest config.

This PR edits _quality-python.yml itself, so every Python member runs this time. That's expected.

Tests

• tests/test_quality_needed.py: covers member code, unrelated changes, root config, another member's lock bump (skip), own transitive dep (run), CI tooling bump (run), and the fail-open cases.
• pytest tests passes; ruff, actionlint and check_workflow_paths.py are clean.