chore: reqstool-regression/python native-package publishing (investigation)

[jimisola]

Context

GitHub Packages does not support hosting PyPI-format packages. The Python "native package" axis of the parameterized regression test matrix is therefore dropped from initial scope.

This ticket tracks the investigation and implementation of a workable alternative, should native-package coverage for Python be needed in the future.

Options

(a) LocalPypiLocation against an in-CI-built wheel
Build the Python wheel in CI, expose as an artifact or temp dir, and consume via reqstool-client's LocalPypiLocation. Tests a different code path than PypiLocation but provides some coverage.

(b) Self-hosted static PyPI index on GitHub Pages
Build the wheel, generate a PEP 503 simple index, and serve from the gh-pages branch of reqstool/reqstool-regression. Consumable via PypiLocation with a custom --index-url. Fully private to the org's domain; never pollutes public PyPI.

(c) TestPyPI
Publish to test.pypi.org. Public but designated for testing. Lightly violates the "no public registries for test fixtures" principle.

Acceptance criteria

• Option selected and documented
• Artifact published and consumable via reqstool-client PypiLocation or LocalPypiLocation
• Python native-package axis implemented and green

Dependencies

• Depends on: feat(workflows): add working-directory input to reusable build/publish workflows .github#35 (if option b requires a publish workflow with working-directory)

Moved from reqstool-client#390.