[ty] Use the top materialization of classes for narrowing in class-patterns for match statements

[AlexWaygood]

Fixes astral-sh/ty#1458

[github-actions]

Diagnostic diff on typing conformance tests

No changes detected when running ty on typing conformance tests ✅

[github-actions]

mypy_primer results

Changes were detected when running on open source projects

Expression (https://github.com/cognitedata/Expression)
- expression/core/result.py:85:73: error[invalid-return-type] Function can implicitly return `None`, which is not assignable to return type `_TSource@default_with | _TSourceOut@Result`
- expression/core/result.py:97:65: error[invalid-return-type] Function can implicitly return `None`, which is not assignable to return type `Result[_TResult@map, _TErrorOut@Result]`
- expression/core/result.py:113:10: error[invalid-return-type] Function can implicitly return `None`, which is not assignable to return type `Result[_TResult@map2, _TErrorOut@Result]`
- expression/core/result.py:125:70: error[invalid-return-type] Function can implicitly return `None`, which is not assignable to return type `Result[_TSourceOut@Result, _TResult@map_error]`
- expression/core/result.py:137:86: error[invalid-return-type] Function can implicitly return `None`, which is not assignable to return type `Result[_TResult@bind, _TErrorOut@Result]`
- expression/core/result.py:177:10: error[invalid-return-type] Function can implicitly return `None`, which is not assignable to return type `Result[_TSourceOut@Result, _TErrorOut@Result]`
- expression/core/result.py:191:23: error[invalid-return-type] Function can implicitly return `None`, which is not assignable to return type `dict[str, _TSourceOut@Result | _TErrorOut@Result | Literal["ok", "error"]]`
- expression/core/result.py:205:23: error[invalid-return-type] Function can implicitly return `None`, which is not assignable to return type `Result[_TErrorOut@Result, _TSourceOut@Result]`
- expression/core/result.py:269:26: error[invalid-return-type] Function can implicitly return `None`, which is not assignable to return type `str`
- expression/core/try_.py:24:26: error[invalid-return-type] Function can implicitly return `None`, which is not assignable to return type `str`
- expression/effect/async_result.py:32:10: error[invalid-return-type] Function can implicitly return `None`, which is not assignable to return type `Result[_TResult@bind, _TError@AsyncResultBuilder]`
- expression/effect/async_result.py:79:94: error[invalid-return-type] Function can implicitly return `None`, which is not assignable to return type `Result[_TSource@AsyncResultBuilder, _TError@AsyncResultBuilder]`
- Found 213 diagnostics
+ Found 201 diagnostics

No memory usage changes detected ✅

[MeGaGiGaGon]

That's fun in the primer seeing a bunch of Expression Result diagnostics going away, since my issue came from also running into this making my own Result type :)