fix(Multivariate): creating an option without default_percentage_allocation returns 500

[bardock-2393]

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Changes

Closes #6615

MultivariateFeatureOptionSerializer.validate() reads attrs["default_percentage_allocation"] directly. The model field has default=100, which makes DRF mark the serializer field required=False, but DRF does not carry a model field's default into validated_data — it only omits the key entirely from attrs if the request doesn't supply it. So POSTing to create a multivariate option without default_percentage_allocation in the payload raised an unhandled KeyError (500) instead of falling back to the model's own default of 100.

Fixed by declaring the field explicitly on the serializer with default=100 (carrying forward the existing min_value/max_value validators), so DRF always populates validated_data with it.

How did you test this code?

Added test_create_mv_option__no_default_percentage_allocation__defaults_to_100, following the existing integration test conventions in test_integration_multivariate.py. Confirmed it reproduces the exact reported KeyError when temporarily reverting the fix, and passes with the fix applied. Ran the full multivariate test suite (65 tests, unit + integration) — all green. Ran make lint and make typecheck — both clean.

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📥 Commits

Reviewing files that changed from the base of the PR and between fc33002 and c63e3a1.

📒 Files selected for processing (2)

• api/features/multivariate/serializers.py
• api/tests/integration/features/multivariate/test_integration_multivariate.py

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📝 Walkthrough

Walkthrough

The multivariate option serializer now defines default_percentage_allocation as an optional float with a default of 100 and bounds from 0 to 100. An integration test verifies that option creation succeeds when the field is omitted and that the stored allocation is 100%.

Estimated code review effort: 2 (Simple) | ~10 minutes

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.57%. Comparing base (fc33002) to head (c63e3a1).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8202      +/-   ##
==========================================
- Coverage   98.71%   98.57%   -0.15%     
==========================================
  Files        1531     1531              
  Lines       61263    61265       +2     
==========================================
- Hits        60475    60390      -85     
- Misses        788      875      +87     

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