[ty] synthesize __setattr__ for frozen dataclasses (#19307)
## Summary
Synthesize a `__setattr__` method with a return type of `Never` for
frozen dataclasses.
https://docs.python.org/3/library/dataclasses.html#frozen-instances
https://docs.python.org/3/library/dataclasses.html#dataclasses.FrozenInstanceError
### Related
https://github.com/astral-sh/ty/issues/111
https://github.com/astral-sh/ruff/pull/17974#discussion_r2108527106
https://github.com/astral-sh/ruff/pull/18347#discussion_r2128174665
## Test Plan
New Markdown tests
---------
Co-authored-by: David Peter <mail@david-peter.de>
