fix: ClassVar[Final[...]] collapses to Any instead of inner type (#21906)

[chenzeyan54-commits]

Summary

Fixes #21906

On Python 3.13+, ClassVar[Final[...]] accepts the annotation (no valid-type
error), but the variable's type still silently collapses to
AnyType(from_error), losing all type information.

Root Cause

In try_analyze_special_unbound_type's FINAL_TYPE_NAMES branch, when
self.allow_final is True (i.e. the nested Final is legitimately
accepted, e.g. inside ClassVar[Final[...]] on 3.13+), the code fell
through to return AnyType(TypeOfAny.from_error) instead of analyzing the
inner type.

Fix

In the same branch, when self.allow_final is True and the Final has
type arguments, preserve and return the inner type by recursing into
anal_type(t.args[0]):

elif not self.allow_final:
    self.fail(
        "Final can be only used as an outermost qualifier ...",
        t, code=codes.VALID_TYPE,
    )
elif t.args:
    # Nested Final[...] is accepted here (e.g. ClassVar[Final[...]] on 3.13+);
    # preserve and return the inner type instead of collapsing to Any.
    return self.anal_type(t.args[0])
return AnyType(TypeOfAny.from_error)

Verification

• Added regression guard testFinalUsedWithClassVarAfterPy313PreservesType in
  test-data/unit/check-final.test — reveal_type(A.cv) reports
  builtins.dict[type[B], __main__.A instead of Any.
• Existing testFinalUsedWithClassVarAfterPy313 (no error) and
  testFinalUsedWithClassVar (3.12 still errors) are unaffected.

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅