More strict types with Pydantic; updated CI

[regularkevvv]

This PR changes some of the typing in the coverage feature to be more string, using Pydantic and updating CI to have the ty check

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Summary by cubic

Strengthened coverage type safety with Pydantic and validated report types, improving config handling and reducing runtime errors. CI now enforces type checks with “uv run ty check”.

• Refactors
  • Added jinjatest.coverage.types with CoverageConfig, ReportType, BranchType, and validators.
  • _load_pyproject_config now returns CoverageConfig with defaults and ignores extra TOML fields; invalid or missing configs fall back safely.
  • Normalizes and validates CLI/config report types; defaults to "term" when none provided.
  • Switched branch_type to BranchType in discovery; exported new types via init; tightened reporter dict typing.
  • Updated CI and publish workflows to run “uv run ty check”.

^{Written for commit 782fa2d. Summary will update on new commits.}

[cubic-dev-ai]

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