chore: Enable ty unused-ignore-comment rule (#762)

## Summary

Now that `ty` supports detecting unused suppression comments (upstream
issues [astral-sh/ty#278](astral-sh/ty#278)
and [astral-sh/ty#1501](astral-sh/ty#1501) are
closed), enable the `unused-ignore-comment` rule project-wide so
obsolete `# ty: ignore[...]` comments are caught automatically.

Verified that all current `# ty: ignore[...]` suppressions in the
codebase are still required (none had to be removed).

Author: vdusek

pyproject.toml

@@ -186,6 +186,9 @@ python-version = "3.11"
 include = ["src", "tests", "scripts", "docs", "website"]
 exclude = ["website/versioned_docs"]
 
+[tool.ty.rules]
+unused-ignore-comment = "error"
+
 [[tool.ty.overrides]]
 include = ["docs/**/*.py", "website/**/*.py"]
 [tool.ty.overrides.rules]