feat: Allow pinning dependency to a specific commit

[BatteredBunny]

• Adds support for pinning to a specific commit via git_tag= or git_commit=
• Sets up infra for pytest tests and adds 2 tests which test tag & commit pinning along with pin changing behaviour.
• Adds github action workflow which runs the tests.
• Fixes infinite recursion bug in mama deploy

For tests it uses https://github.com/BatteredBunny/MamaExampleRemote repo since the original was missing tags to test.

[RedFox20]

Looks mostly good to me, I think this can be squashed and merged

[Copilot]

Pull request overview

Adds git dependency pinning improvements (including commit-hash pin behavior), introduces a pytest-based test suite to validate git pinning and papa deploy/parse flows, and wires CI to run tests. Also includes a fix intended to prevent infinite recursion during directory copy operations.

Changes:

• Extend git dependency handling to support treating hex strings as commit pins and improve fetch/checkout behavior for tag/branch/commit transitions.
• Add pytest test infrastructure + multiple integration-style tests for pinning, pin changes, papa deploy/parse, and stale dependency recovery.
• Add a GitHub Actions workflow to run tests, plus documentation updates and minor test-project CMake adjustments.

Reviewed changes

Copilot reviewed 23 out of 24 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
mama/types/git.py	Updates git fetch/checkout logic; adds helpers for hex detection and status formatting.
mama/util.py	Attempts to prevent recursive copying by skipping the output directory during os.walk.
pyproject.toml	Configures pytest to discover tests under tests/.
tests/conftest.py	Adds tests/ to sys.path to allow import testutils.
tests/testutils.py	Adds shared test helpers for shelling out, filesystem checks, and platform detection.
tests/test_git_pinning/*	Adds integration test + mamafile for tag/commit pinning behavior.
tests/test_git_pin_change/*	Adds integration test + mamafile to validate switching pins across commits/tags/branches.
tests/test_stale_dep/*	Adds integration test + mamafile to simulate a stale dependency and validate updating.
tests/test_papa_deploy/*	Adds integration test + minimal C++/CMake consumer to validate deploy output.
tests/test_papa_parse/*	Adds parsing test + sample papa.txt.
tests/test/example_library/*	Updates test library to std::filesystem and bumps CMake/C++ standard settings.
tests/test/example_consumer/*	Adjusts workspace + pins a git dependency commit; simplifies CMake target sources.
README.md	Adds contributor test-running instructions and minor whitespace fixes.
.gitignore	Ignores packages/ and bin/ build artifacts.
.github/workflows/tests.yml	Adds CI workflow to run pytest.

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