chore: switch to ty type checker

[zzstoatzz]

summary

• switches from mypy to ty for type checking in pre-commit
• ty is astral's new extremely fast python type checker written in rust (10-60x faster than mypy/pyright)
• keeps mypy for pytest-mypy-plugins typesafety tests in tests/typesafety/

approach

starting with permissive rules - all ~1100 existing errors are ignored for now and can be gradually enabled as we fix them.

fast-follow PRs

here's a breakdown of the error categories, roughly in order of ease/impact:

1. invalid-parameter-default (71 errors) - easy wins

mostly fastapi endpoints with param: SomeFilter = None that should be param: SomeFilter | None = None:

# before
artifacts: filters.ArtifactFilter = None

# after  
artifacts: filters.ArtifactFilter | None = None

2. unresolved-import (18 errors) - conditional imports

imports inside try/except blocks for optional dependencies (pendulum, logfire, apprise plugins). ty doesn't understand these are guarded - may need # ty: ignore comments or restructuring.

3. invalid-assignment (95 errors) - mixed bag

• monkey-patching __init__ in deprecation decorators (~10 errors)
• dict subscript assignments where ty infers wrong types
• implicit shadowing of class attributes

4. invalid-return-type (134 errors) - generic type issues

many in _internal/concurrency/ where Call[T].result() returns T but ty infers Unknown. likely needs better type annotations on the Call class.

5. invalid-argument-type (370 errors) - largest category

• callable/generics confusion in concurrency code (cast_to_call, call_soon_in_*)
• httpx client method signatures
• pydantic model validation where ty doesn't understand validators

6. unresolved-attribute (134 errors) - dynamic attributes

• __name__ on wrapped functions - ty doesn't understand @wraps
• private methods on type objects - Block class introspection
• sys.maxint in vendored croniter (py2 compat)
• module-level private attrs (threading._register_atexit)

7. possibly-missing-attribute (139 warnings) - optional checks

Optional[X] used without None checks. mostly in task/flow engine code where we know the attribute exists at runtime.

8. invalid-method-override (23 errors) - inheritance issues

subclasses with incompatible method signatures. needs investigation.

9. other smaller categories

• non-subscriptable (27) - likely type annotation issues
• invalid-await (25) - async/sync confusion in type stubs
• no-matching-overload (18) - overload resolution failures

changes

• adds ty>=0.0.2 to dev dependencies
• adds [tool.ty] config to pyproject.toml with permissive rules
• replaces mypy pre-commit hook with ty local hook
• updates mypy config comment to clarify it's kept for typesafety tests

testing

# verify ty passes
uv run ty check

# verify typesafety tests still work  
uv run pytest tests/typesafety/ -v

references

• https://astral.sh/blog/ty
• https://github.com/jlowin/fastmcp (example adoption)

🤖 Generated with Claude Code

[codspeed-hq]

Merging this PR will not alter performance

Summary

✅ 2 untouched benchmarks

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_{Comparing chore/switch-to-ty (5015e20) with main (600a6a7)}

[github-actions]

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