chore(mypy): drop vestigial tornado ignore_missing_imports override

[jd]

Tornado ships a py.typed marker, so its types resolve without help.
The override was silently downgrading every tornado symbol to Any if
the package ever went missing, instead of failing loudly.

mypy still reports no issues with the override removed.

[jd]

This pull request is part of a Mergify stack:

#	Pull Request	Link
1	chore(mypy): drop vestigial tornado ignore_missing_imports override	#676	👈
2	fix: annotate wait_base.radd as taking the int seed from sum()	#677
3	chore(mypy): enable the strictness options strict leaves off	#678
4	refactor: drop always-true truthiness checks and enable truthy-bool	#679
5	refactor: declare BaseAction's REPR_FIELDS and NAME as ClassVar	#680
6	test: fix possibly-undefined and deprecated call sites	#681
7	refactor: mark overridden methods with @OverRide	#682

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-08-05 15:24 UTC · Rule: default · triggered by rule autoqueue
• ✅ Checks skipped · PR is already up-to-date
• ✅ Merged — 2026-08-05 15:24 UTC · at bc8baca3b8b0f2a0a579c5614f86ac4e880e8ade · squash

This pull request spent 8 seconds in the queue, including 1 second running CI.

Required conditions to merge

• github-review-approved [🛡 GitHub branch protection]
  • chore(mypy): drop vestigial tornado ignore_missing_imports override #676