Dependency updates

[jonchang]

Note

Refreshes dev dependency set in poetry.lock.

• Upgrades mypy to 1.19.1 and adds new runtime dependency librt (non-PyPy platforms)
• Bumps test/docs/tooling: coverage (7.13.1), pytest (9.0.2), mkdocs-material (9.7.1; now requires requests >= 2.30), pymdown-extensions (10.20), mkdocstrings-python deps unchanged
• Updates utility libs: pathspec (1.0.3; new extras), platformdirs (4.5.1), gitpython (3.1.46), hypothesis (6.150.2), certifi (2026.1.4)

Scope: lockfile-only version bumps; no application code changes.

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