Related Issue: https://github.com/j178/prek/issues/1685
## Summary
prek can now be run with python -m prek in addition to the prek command,
matching common Python CLI tools like `black`, `ruff`, and `uv`.
## Motivation
- Consistency: Many Python tools support python -m <package>
- Virtual environments: Makes it clear which Python interpreter (and
venv) is used
- Scripts & CI: Explicit execution environment
- Tool integration: Some tools only support the `python -m` form
## Changes
- Add `python/prek/` package with `__init__.py` and `__main__.py`
- Set python-source = "python" in `pyproject.toml` so maturin includes
the Python package
- `__main__.`py invokes the prek binary next to the Python executable
(e.g. `.venv/bin/prek with .venv/bin/python`), falling back to PATH if
not found
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Co-authored-by: Jo <10510431+j178@users.noreply.github.com>
