A class-level __qualname__ binding that CPython rejects at class creation is accepted #982

Summary

pycc accepts two class bodies that CPython rejects at class-creation time, both
involving a class-level binding named __qualname__. This is a D-198 false
acceptance in both shapes.

Split out of #980 (which fixes @property def __slots__ only). #980's guard is
value-independent by construction (D-236), and the attribute half of
__qualname__ is value-typed — so it cannot live in that guard and needs its
own generating rule plus its own ADR.

Reproductions (CPython 3.13.9, v3.13.9:8183fa5e3f7)

1. Property route

class C:
 @property
 def __qualname__(self) -> int:
 return 1

CPython: TypeError: type __qualname__ must be a str, not property, raised while
the class statement executes. pycc: accepted, runs, prints 1.

2. Attribute route, non-str value

class D:
 __qualname__: int = 1

CPython: TypeError: type __qualname__ must be a str, not int, raised while the
class statement executes. pycc: accepted, runs.

3. Attribute route, str value — agrees, must stay accepted

class D:
 __qualname__: str = "D"

CPython: exit 0. pycc: exit 0. This is the negative case: any fix must not
over-reject it.

Why this is not folded into #980

type.__new__ validates the type of __qualname__ rather than merely
consuming it, so the correct rule is value-typed ("__qualname__ must be bound
to a str"), not name-based. D-236's reject_reserved_class_attr_name runs
before any value extraction precisely so every class-body route can call it at
the same cheap, value-independent point; adding a value-typed name there would
break that invariant. Closing only the property half would leave the name
half-closed under a rule that does not describe it.

Acceptance criteria

• @property def __qualname__ is rejected with a message whose account is
  type.__new__'s __qualname__ type check at class creation.
• __qualname__: int = 1 (and other non-str bindings) is rejected on the
  attribute route.
• __qualname__: str = "D" stays accepted (negative test).
• Unit + e2e coverage for each shape, 100% line/region coverage (D-014).
• Either a new ADR for the value-typed generating rule, or a recorded
  amendment to D-236 explaining why one is not needed.
• Replace the deferral pin a_property_getter_named_qualname_is_left_to_issue_<this>
  in crates/pycc_hir/src/tests/reserved_dunder_class_attrs.rs.

Pointers

• crates/pycc_hir/src/class/reserved_names.rs
• crates/pycc_hir/src/class/body.rs (MethodKind::PropertyGetter arm)
• docs/decisions/D-236-reject-a-class-attribute-named-after-the-instantiation.md