brain/dataclasses: add inference tip for dataclasses.replace()

[ego-ipse]

Summary

dataclasses.replace(obj, **changes) was inferred by following the stdlib
body of replace() / _replace(). That body resolves obj.__class__ via
the metaclass chain, which trips when obj is an instance of a class whose
bases include a subscripted generic (e.g. IrCollection(Base[T])) — the
Subscript node causes helpers.object_type to return Uninferable,
propagating up to the entire replace() call.

The same bug manifests differently for old-style Generic[T] vs PEP 695
class Foo[T] syntax: old-style returns Uninferable (masked error), PEP 695
returns the wrong class (visible false positives in pylint E1101).

Fix

Add a dedicated inference tip for dataclasses.replace in
brain_dataclasses.py that short-circuits the stdlib body entirely: it infers
the first argument, determines its type, and yields a fresh instance of that
class. This is the same pattern used by other brain plugins (isinstance,
type(), etc.) and correctly propagates the concrete caller type through
replace() — including across Self-annotated method chains.

The tip handles both call forms:

• dataclasses.replace(obj, ...) (attribute access)
• from dataclasses import replace; replace(obj, ...) (bare name)

Tests

Nine new tests in tests/brain/test_dataclasses.py:

Test	What it covers
test_replace_returns_instance_of_caller_type	Basic case: result is the passed type
test_replace_returns_subclass_instance	old-style Generic[T] base — concrete subclass propagated
test_replace_pep695_generic_base	PEP 695 class Base[T] — same (skipped on <3.12)
test_replace_bare_name_form	from dataclasses import replace form
test_replace_frozen_dataclass	frozen=True is orthogonal, still works
test_replace_uninferable_first_arg	First arg can't be inferred → yields Uninferable
test_replace_classdef_first_arg	First arg is a class itself → yields instance of it
test_replace_non_instance_non_class_falls_back	First arg infers to a module → falls back to default inference
test_replace_no_args_does_not_crash	Edge case: no args, no uncaught exception