[ty] Fix incorrect docstring in call signature completion

[MichaReiser]

Summary

This PR fixes astral-sh/ty#1071

The core issue is that CallableType is a salsa interned but Signature (which CallableType stores) ignores the Definition in its Eq and Hash implementation.

This PR tries to simplest fix by removing the custom Eq and Hash implementation. The main downside of this fix is that it can increase memory usage because CallableTypes that are equal except for their Definition are now interned separately.

The alternative is to remove Definition from CallableType and instead, call bindings directly on the callee (call_expression.func). However, this would require
addressing the TODO

here

ruff/crates/ty_python_semantic/src/types.rs

Lines 4582 to 4586 in 39ee71c

	// Most class literal constructor calls are handled by `try_call_constructor` and
	// not via getting the signature here. This signature can still be used in some
	// cases (e.g. evaluating callable subtyping). TODO improve this definition
	// (intersection of `__new__` and `__init__` signatures? and respect metaclass
	// `__call__`).

This might probably be worth addressing anyway, but is the more involved fix. That's why I opted for removing the custom Eq implementation.

We already "ignore" the definition during normalization, thank's to Alex's work in #19615

Test Plan

Screen.Recording.2025-08-21.at.14.21.06.mov

[github-actions]

Diagnostic diff on typing conformance tests

No changes detected when running ty on typing conformance tests ✅

[github-actions]

mypy_primer results

No ecosystem changes detected ✅
No memory usage changes detected ✅

[AlexWaygood]

Makes sense to me!

I agree that we need to do some work cleaning up Type::bindings(), but I think both @sharkdp and I have tried several times at this point and every time we found it surprisingly hard 🙃 so this is definitely the easier fix for now.

[Gankra]

Nice!

[MichaReiser]

I'll give @carljm a chance to chime in, as he reasoned that we should remove Definition from CallableType.

[carljm]

I'll give @carljm a chance to chime in, as he reasoned that we should remove Definition from CallableType.

I do think that's what we should do eventually, but it doesn't have to be done right now -- this fix improves the behavior in the short term and I don't think makes anything more difficult for removing the definition in future, so I'm in favor of it.

(Also it removes code, and all else equal I'm always in favor of that 😆 )

[Gankra]

I'm gonna land this since it's a important/pervasive bugfix, makes it easier to test/debug other function handling features.