ci: drop Python 3.10 from CI matrix and minimum version (#240)

[Olen]

Summary

Closes #240. Python 3.10 reaches EOL in October 2026 (~5 months from now). This PR drops it from both the CI matrix and `pyproject.toml`'s minimum, so the package doesn't claim support for a version we no longer test against.

Changes

• `.github/workflows/python-package.yml` — matrix becomes `["3.11", "3.12", "3.13", "3.14"]`.
• `pyproject.toml` — `python = ">=3.10"` → `">=3.11"`, `tool.ruff.target-version` = `"py310"` → `"py311"`.

What ruff check --fix did

Nothing. The codebase was already using modern syntax (PEP 604 unions like `X | None`, `from future import annotations` everywhere, no `typing.Optional` or `typing.Union` left), so bumping the target version unlocks future rule additions but doesn't rewrite anything today. Net diff: 3 insertions, 3 deletions across 2 files.

Why bundle pyproject + workflow in one PR

If we dropped 3.10 from CI but left `python = ">=3.10"` in pyproject, the package would still claim to support a version we no longer test — and a 3.10-specific regression could land silently. Either drop both, or drop neither.

Side benefit

The smallest matrix entry was contributing to today's earlier transient CI failure on #241 (ruff 0.15.13 was published with wheels for 3.12/3.14 but not yet for 3.10/3.11/3.13). Dropping 3.10 doesn't fix that class of issue entirely, but it does shrink the matrix by 20% which means one fewer chance of hitting a partial-wheel-rollout edge case.

Test plan

• Local `pytest` — 23 tests pass
• Local `ruff check` — clean (target now `py311`)
• Local `ruff format --check` — clean
• Local `ruff check --fix` — no changes proposed (code already modern enough)
• CI: 4-version matrix green
• Merge order: this PR first, then rebase docs+fix: expand docstrings, sanitise AuthenticationError message #241 on top to pick up the 4-version matrix

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