Add requires-python >=3.10 to pyproject.toml

[yashb98]

Summary

Fixes #1302.

pyproject.toml has no requires-python, so pip resolves and installs liger-kernel on any interpreter. Users on unsupported Pythons get runtime failures instead of a clean "requires Python >= X" resolver message.

This adds requires-python = ">=3.10", matching the project's own floor: every CI test workflow (nvi-ci, amd-ci, checkstyle, benchmark) and the release-publish workflow run Python 3.10.

Picking up the hand-off from #1307 (closed by its author due to inactivity, fix noted as still valid).

Testing Done

Metadata-only change. Verified the line parses and the floor matches CI:

$ python -c "import tomllib; print(tomllib.load(open('pyproject.toml','rb'))['project']['requires-python'])"
>=3.10

[yashb98]

Same as #1328, the workflow runs here are held at action_required and have never run. Could a maintainer approve them?