refactor: Implement @with_metadata decorator to reduce boilerplate

[gagantrivedi]

This is a POC to solve #6277

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• [ ] I have added information to docs/ if required so people know about the feature!
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Changes

Introduces a decorator pattern to automatically handle metadata in serializers, eliminating the need to manually override create(), update(), and validate() methods.

Changes:

• Add @with_metadata decorator in metadata/serializers.py
• Add helper functions _validate_required_metadata_for_model and _update_metadata_for_instance
• Refactor FeatureSerializerWithMetadata to use decorator pattern
• Reduce boilerplate

Benefits:

• Eliminates fragility: impossible to forget create() override
• No MRO issues: decorator works regardless of inheritance order
• More maintainable: metadata logic centralized in one place
• More explicit: @with_metadata makes intent clear

How did you test this code?

Please describe.

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