Labelformat: Add python 3.14 support

[MalteEbner]

What has changed and why?

Add python 3.14 support:

• Update Readme, docs
• Update CI to test on python 3.14
• Relax requirement for pydantic and pedantic-xml to support newer pypi versions, which then support python 3.14
• Upgrade pytest to v8, otherwise it errors on python 3.14
• Add two casts in code to make mypy succeed on python 3.14

How has it been tested?

• Manually
• CI

[MalteEbner]

/review

[Copilot]

Pull request overview

This PR updates labelformat to support Python 3.14 by refreshing dependency constraints, documentation, and CI so the project can install and test cleanly on newer Python versions.

Changes:

• Update runtime/dev dependency constraints (notably pydantic, pydantic-xml, pytest) and refresh uv.lock accordingly.
• Update docs/README to state Python 3.8–3.14 support.
• Update GitHub Actions CI to run tests on Python 3.14.

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
uv.lock	Updates locked dependency resolutions to include versions compatible with newer Python (incl. 3.14).
pyproject.toml	Adds Python version classifiers and relaxes dependency pins (incl. pytest>=8).
docs/installation.md	Updates stated supported Python versions.
docs/index.md	Updates stated supported Python versions and minor formatting tweak.
docs/features.md	Updates stated supported Python versions and minor formatting tweak.
README.md	Updates stated supported Python versions and the example uv sync command.
.github/workflows/run-tests.yml	Updates CI Python matrix to include 3.14.

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[IgorSusmelj]

LGTM