This PR:
- documents the pending Python `0.14.0` and `0.15.0` releases in
`python/CHANGELOG.md`
- aligns `python/composio/__version__.py` with `python/pyproject.toml`
at `0.15.0`
- adds a release guard so Python package/provider versions, runtime
version, and changelog entries cannot drift silently
- leaves Python release tags and PyPI publishing untouched; `py@0.14.0`
should still be published before `py@0.15.0`