feat(python): add the python port of trackparse

[4matic]

Summary

Adds the Python port: the PyPI package trackparse for Python 3.9+, with zero dependencies. It passes all 11,891 shared fixtures, and its output is byte-identical to JS: scripts/compare-ports.mjs diffs the full JSON of every fixture case across both ports and finds 0 differences.

from trackparse import parse
t = parse("Wilkinson ft. Becky Hill - Afterglow (Sub Focus VIP Remix)")
t.artists[1].role        # 'featured'
t.versions[0].modifiers  # ('vip',)
t.to_dict()              # the spec's camelCase JSON, identical to JS

Commits (please use Rebase and merge, so release-please lists each one in the changelog)

• feat(spec): R0.6 now defines a letter as Unicode general category L (JS \p{L}, Python isalpha()). Two new fixtures pin the change.
• fix(js): a malformed knownArtists or keyword option threw a TypeError, which breaks R0.8. Found in code review; Python already handled it.
• perf(js): trailing junk stripping (R8.4) was quadratic. A 40k-character input took about 1.7 s and now takes about 35 ms. Both ports have a regression test.
• feat(python): the port itself (python/), CI, release wiring and docs.

Python package

• src/trackparse/ mirrors js/src module for module, with the same rule-ID comments. Results are frozen dataclasses with snake_case attributes, and to_dict()/from_dict() convert to and from the spec JSON.
• API: parse, parse_artists, format_track, normalize, all_artists, create_parser, SPEC_VERSION, __version__.
• Tests: 991 pytest tests covering every fixture, schema validation of every output, Hypothesis versions of the spec invariants, and the API.

CI and release

• python.yml: ruff, mypy --strict and pytest on Python 3.9–3.14. A build job installs the wheel into a clean venv and runs conformance.py --strict against it.
• spec.yml: checks that the js, spec and python versions all match.
• release-please: python joins the linked group, so the next release is 0.2.0 for js, spec and python. release.yml has a new publish-pypi job that uses trusted publishing (environment pypi).
• Docs: AGENTS.md, README (Python install and quick start, PyPI badges), python/README.md (the PyPI page), .github/release-notes/0.2.0.md.

Before merging the release PR

The PyPI pending publisher must exist: project trackparse, owner 4matic, repo trackparse, workflow release.yml, environment pypi.

Test plan

• JS: 981 tests; compat on the ESM and CJS builds, 11,891/11,891
• Python: 991 tests on 3.9, 3.12 and 3.13; ruff, mypy --strict, gen_data check; wheel conformance at 100%
• compare-ports.mjs: 0 differences across all 11,891 cases
• actionlint; fixture validation; gen:check
• CI green on this PR