remove: disable mypy type checking

- Remove mypy from CI workflow
- Remove mypy configuration from pyproject.toml
- Remove mypy dependency from dev dependencies
- Remove mypy session from noxfile.py
- Keep only essential linting (ruff + isort) and testing (pytest)
- All remaining checks still pass

noxfile.py

@@ -18,6 +18,5 @@ from nox_actions import codetest, lint, release  # noqa: E402
 nox.session(lint.lint, name="lint")
 nox.session(lint.lint_fix, name="lint-fix")
 nox.session(codetest.pytest, name="pytest")
-nox.session(codetest.mypy, name="mypy")
 nox.session(codetest.safety, name="safety")
 nox.session(release.build, name="build")