Use ty instead of mypy for type checking

[jbcoe]

closes #9

[Copilot]

Pull request overview

This PR replaces mypy with ty as the project's type checker and updates dependency management and CI to match.

Changes:

• Update development dependencies in pyproject.toml and uv.lock to remove mypy (and its supporting packages) and add ty.
• Configure ty in pyproject.toml with an override for py_cppmodel.py to ignore unresolved-attribute diagnostics.
• Update local test script and GitHub Actions workflow to run uv run ty check . instead of mypy, and simplify the CI Python setup step.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated no comments.

File	Description
uv.lock	Regenerates the lockfile to remove mypy, mypy-extensions, librt, and pathspec, and add ty along with updated dev dependency metadata for the project.
pyproject.toml	Switches the dev type-checking dependency from mypy to ty and adds a tool.ty override for py_cppmodel.py to ignore unresolved attribute diagnostics.
test.macos.sh	Updates the local test script to run uv run ty check . instead of uv run mypy *.py --check-untyped-defs.
.github/workflows/python.yml	Adjusts the CI workflow to use ty for type checking and relies on setup-uv for Python installation without an extra uv python install step.

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