✨ feat: support Python 3.15 and 3.15t, drop Python 3.10

[ShigureNyako]

Summary

• Raise the template's minimum Python version to 3.11 and align its classifiers, Ruff target and lockfile. Preserve support and CI coverage for 3.11–3.14.
• Add Python 3.15 and free-threaded 3.15t to the regular unit-test matrix, including prereleases. Both use the normal dependency installation and complete test suite, without skips or allowed failures.
• Bind uv to each unit-test matrix interpreter so the 3.15t job uses the free-threaded interpreter rather than falling back to a regular build.
• Regenerate the lockfile without upgrading dependencies; this only removes the now-unused Python 3.10 backports. The template has no runtime dependencies or Pydantic gate.

Validation

Locally on macOS arm64:

• UV_PYTHON=<version> UV_LOCKED=true just ci-install ci-test: passed on 3.11.16, 3.12.14, 3.13.15, 3.14.7, 3.15.0rc2 and 3.15.0rc2 free-threaded (1 test each).
• Minimum-version just ci-lint ci-fmt-check: passed.
• sdist/wheel builds on all six interpreters: passed; inspected wheel metadata for Requires-Python: >=3.11 and the updated classifiers.
• Clean wheel installations and both moelib --version / python -m moelib --version on 3.11, 3.15 and 3.15t: passed. Verified the GIL remains disabled after imports on 3.15t.
• uv lock --check, workflow formatting and git diff --check: passed.

Review follow-up

In cad2244, removed the extra README paragraph, runtime-assertion step, lint job environment overrides and CI lock-policy change. Only the unit-test interpreter selection remains, to ensure 3.15t actually runs free-threaded Python.

All seven checks pass on cad2244: unit tests, Python 3.11–3.15 and 3.15t and lint/format. The 3.15t job log confirms the free-threaded interpreter and the complete passing test suite.

Repository settings

Rechecked after review: the repository ruleset now requires the 3.11–3.15 and 3.15t unit-test checks, with no obsolete 3.10 requirement. No repository settings were changed by this PR.

@SigureMo please review when convenient.

[SigureMo]

说明必要性

[ShigureNyako]

这两项对 lint job 并非必需：setup-python 已将普通 3.11 放到 PATH 首位；UV_LOCKED 是额外的 CI 策略，不是版本兼容修复。已在 cad2244 删除 lint 的整个 env，并删除 unit-test 的 UV_LOCKED。仅在 unit-test 保留 UV_PYTHON 来显式选择 3.15t：本地将 free-threaded 解释器目录放到 PATH 首位后，未指定版本的 uv venv 仍选择 3.14；设置 UV_PYTHON=3.15t 才选择 free-threaded 解释器。

[SigureMo]

LGTMeow