fix(utils): walk MRO in get_class_field_annotations

[allmonday]

Summary

• get_class_field_annotations previously read only cls.__dict__['__annotations__'], missing fields inherited from parents.
• This broke copy_dataloader_kls: the generated class NewLoader(Parent): pass has empty __annotations__ in its own __dict__, so _create_loader_instance could not see or inject the parent's loader params (user_id, permission, etc.), raising AttributeError at runtime.
• Now walks cls.__mro__ and merges annotations from every class in the chain. The same fix also corrects the _context detection in analysis.py:385, so copies of context-aware loaders are now correctly recognized.

Why explicit MRO walk (not cls.__annotations__.keys())

Python's attribute lookup returns the first __annotations__ found in the MRO. So:

class Parent: user_id: int
class Mixin(Parent): extra: str
Mixin.__annotations__  # {'extra': str} — loses user_id

The explicit reversed-MRO loop merges across all levels, which is what loader param injection needs.

Side-effect check: DataLoader's own annotated fields

Walking the full MRO also surfaces aiodataloader.DataLoader's own annotations (batch, cache, max_batch_size). These all have class-level defaults, so _create_loader_instance skips them via its existing has_default and field not in param_config branch — no behavior change.

Test plan

• Updated test_get_class_field_annotations_with_inheritance — derived class now includes base field
• Updated test_get_class_field_annotations (test_utils.py) — D(C) and E(C) now reflect inherited hello
• Added test_get_class_field_annotations_subclass_with_no_own_fields — covers class Child(Parent): pass
• Added test_copy_dataloader_kls_inherits_parent_annotations — regression for the reported bug
• Full suite: 707 passed, 1 skipped

🤖 Generated with Claude Code