Add Python 3.14 to CI matrix and sync version metadata

[hartym]

Problem

Python 3.14 is the current stable CPython release, but the project does not test against it, and some version metadata is out of date.

CI does not test 3.14. Both .github/workflows/ci.yml (test job) and .github/workflows/release.yml (test-package job) pin the matrix to ['3.10', '3.11', '3.12', '3.13']. requires-python is >=3.10 with no upper bound, so 3.14 is implicitly supported but never exercised.

Stale metadata:

• classifiers.txt lists Python 3.5, 3.6, 3.7 and omits 3.10 to 3.14.
• docs/release.rst states the release workflow tests on Python 3.10-3.13.

Fix

• Add '3.14' to both test matrices.
• Update classifiers.txt to list 3.10 to 3.14.
• Update the version range in docs/release.rst.

The suite passes locally on supported interpreters.