Add Python 3.15 support

[CarlKCarlK]

Track support for Python 3.15 in bed-reader.

Scope:

• Update Python classifiers and any version constraints.
• Add Python 3.15 to CI and wheel/artifact verification.
• Exercise both the Python API and Rust-backed paths on Python 3.15.

Version policy:

• Target Python 3.12-3.15 for the release adding Python 3.15.
• Drop Python 3.10, whose end of life is expected around October 2026, and Python 3.11 in line with Scientific Python SPEC 0's three-year support window.
• Revisit the floor annually: add the newest Python and drop versions outside that three-year window.
• Reassess dependency minimums and remove compatibility constraints that exist only for Python 3.10 or 3.11.

Release workflow modernization:

• Bring publication workflow up to the current FaST-LMM/PySnpTools standard.
• Add a tag-triggered release workflow that verifies the tag matches the package version.
• Run the Rust test/clippy checks and Python test suite against the tagged source.
• Build the maturin wheels and sdist, then clean-install and smoke-test the exact artifacts before publication.
• Validate the wheel rebuilt from the sdist and fail on mismatches.
• Publish to PyPI only after artifact tests pass, using Trusted Publishing and attestations.
• Pin action/tool versions consistently with the modern workflows.
• Decide separately whether the corresponding Rust crate should be published from the same release and add an explicit crates.io validation/publication step if so.
• Resolve and enforce the Python/Rust package version relationship before release.