Fix Python 3.9: _get_class_annotations inherits parent annotations via getattr MRO traversal

[Copilot]

In Python 3.9, getattr(cls, '__annotations__') traverses the MRO and returns a parent class's annotations dict when the child declares none. Python 3.10+ fixed this to return {} instead — causing _class_to_schema() to silently include inherited fields only on 3.9.

Changes

• _get_class_annotations: Added an object-identity guard after the getattr fallback. If the returned mapping is the same object (is) as any base class's own __annotations__, it's MRO-inherited and we return {} instead.
• Preserves the getattr fallback for metaclass-defined __annotations__ properties (lazily computed annotations), since those return a freshly constructed dict each time — never is-identical to a base class's annotations.

class Base:
    x: int

class Child(Base):
    role = v.str()  # no own annotations

schema = _class_to_schema(Child)
# Before (Python 3.9): {"role": ..., "x": ...}  ← 'x' leaked from Base
# After:               {"role": ...}             ← only own fields

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