fix Preserve class-scoped type parameters when converting __new__ to a callable #4267

[asukaminato0721]

Summary

Fixes #4267

Bare generic classes now preserve class-scoped type parameters when converting __new__ to a callable.

Class8 correctly infers Class8[str] and rejects inconsistent constructor arguments.

Test Plan

Added regression coverage and updated generated conformance results.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

rotki (https://github.com/rotki/rotki)
+ ERROR rotkehlchen/db/settings.py:286:60-92: `frozenset[_T_co]` is not assignable to `frozenset[ExchangeLocationID]` [bad-assignment]

scikit-build-core (https://github.com/scikit-build/scikit-build-core)
+ ERROR src/scikit_build_core/build/_wheelfile.py:74:30-74: `frozenset[_T_co]` is not assignable to `AbstractSet[Tag]` [bad-assignment]

streamlit (https://github.com/streamlit/streamlit)
+ ERROR lib/streamlit/runtime/scriptrunner_utils/script_requests.py:61:45-77: `frozenset[_T_co]` is not assignable to `frozenset[str]` [bad-assignment]
+ ERROR lib/streamlit/runtime/scriptrunner_utils/script_run_context.py:209:45-77: `frozenset[_T_co]` is not assignable to `frozenset[str]` [bad-assignment]

ibis (https://github.com/ibis-project/ibis)
- ERROR ibis/expr/types/relations.py:4963:21-68: `list[tuple[Unknown, ...]]` is not assignable to variable `names` with type `Iterable[str] | None` [bad-assignment]
+ ERROR ibis/expr/types/relations.py:4963:21-68: `list[tuple[str, ...]]` is not assignable to variable `names` with type `Iterable[str] | None` [bad-assignment]