fix: use __dict__ lookup in _get_class_flags to fix diamond inheritan…

[WHOIM1205]

Fix incorrect tag/config resolution in diamond inheritance

Summary

_FlagManager._get_class_flags currently uses hasattr and getattr when iterating over the class MRO.
Because getattr follows Python's full attribute lookup chain, classes that do not define _tags (or _config) themselves may still return values inherited from ancestors.

In diamond inheritance scenarios this can re-apply ancestor flags later in the merge order and overwrite overrides coming from mixins.

Example

class A(BaseObject):
    _tags = {"handles_missing_data": False}

class MissingDataMixin(A):
    _tags = {"handles_missing_data": True}

class MyBase(A):
    pass

class Concrete(MyBase, MissingDataMixin):
    _tags = {"custom_flag": True}

Concrete().get_tag("handles_missing_data")

[fkiraly]

Good catch. I assume an AI caught this.

Can you please make sure to:

• remove the AI generated comment and leave the old comment there
• fix the issue title