## Summary
Fixes https://github.com/astral-sh/ty/issues/1409
This PR allows `Final` instance attributes to be initialized in
`__init__` methods, as mandated by the Python typing specification (PEP
591). Previously, ty incorrectly prevented this initialization, causing
false positive errors.
The fix checks if we're inside an `__init__` method before rejecting
Final attribute assignments, allowing assignments during
instance initialization while still preventing reassignment elsewhere.
## Test Plan
- Added new test coverage in `final.md` for the reported issue with
`Self` annotations
- Updated existing tests that were incorrectly expecting errors
- All 278 mdtest tests pass
- Manually tested with real-world code examples
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Co-authored-by: Carl Meyer <carl@astral.sh>
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