fix: annotate context managers with Generator for ty 0.0.85

[lesnik512]

Summary

Closes #102

ty 0.0.85 ships a typeshed that deprecates the contextmanager overload for functions annotated -> Iterator[T], so ty check reported two warnings in faststream_redis_timers/testing.py and the scheduled lint run failed. The two methods now return Generator[None]. It is imported from collections.abc because typing.Generator needs all three type arguments before Python 3.13.

Changes

• TestTimersBroker._patch_producer and _patch_broker are annotated -> Generator[None] instead of -> Iterator[None].

Checklist

• Lint and format pass (ruff)
• Type check passes (ty)
• Tests pass and new behavior is covered
• Build succeeds (uv build) if packaging or build config changed
• Repo metadata stays consistent across the three surfaces (GitHub description, pyproject description, profile blurb) if this touches packaging