Revisit type: ignore comments once `ty` supports unused ignore detection

[vdusek]

Currently, ty does not report when a # type: ignore comment becomes obsolete or unused.

Relevant upstream issues:

• Make unused-ignore-comment enabled by default astral-sh/ty#278
• Auto-remove unused type: ignore astral-sh/ty#1501

Revisit existing # type: ignore comments in ~2 months (or once the upstream issues are resolved) and remove any that are no longer necessary once ty supports unused/obsolete ignore detection.

Based on #1625 (comment).