[ty] Fix ClassLiteral.into_callable for dataclasses

[MatthewMckee4]

Summary

Slightly refactor ClassLiteral.into_callable to also look for __init__ functions of type Type::Callable to fix the issue with dataclasses, as the synthensized init created by dataclass isn't covered as it isn't FunctionLiteral

Fixes astral-sh/ty#760

Test Plan

Add subtype test from the issue

[github-actions]

mypy_primer results

Changes were detected when running on open source projects

strawberry (https://github.com/strawberry-graphql/strawberry)
- error[invalid-assignment] strawberry/codegen/query_codegen.py:648:13: Object of type `<class 'GraphQLOptional'> | ((t) -> Unknown)` is not assignable to `((Unknown, /) -> Unknown) | None`
- error[invalid-assignment] strawberry/codegen/query_codegen.py:656:13: Object of type `<class 'GraphQLList'> | ((t) -> Unknown)` is not assignable to `((Unknown, /) -> Unknown) | None`
- error[invalid-parameter-default] strawberry/codegen/query_codegen.py:760:9: Default value of type `<class 'GraphQLObjectType'>` is not assignable to annotated parameter type `(str, /) -> GraphQLObjectType`
- Found 359 diagnostics
+ Found 356 diagnostics

bokeh (https://github.com/bokeh/bokeh)
- error[invalid-argument-type] src/bokeh/embed/bundle.py:186:29: Argument to function `__new__` is incorrect: Expected `(str, /) -> Unknown`, found `<class 'URL'>`
- error[invalid-argument-type] src/bokeh/embed/bundle.py:189:30: Argument to function `__new__` is incorrect: Expected `(str, /) -> Unknown`, found `<class 'URL'>`
- Found 858 diagnostics
+ Found 856 diagnostics

No memory usage changes detected ✅

[sharkdp]

Thank you very much!

Made a minor change to avoid one unnecessary clone.