feat: add serving_size and serving_quantity to OFF index schema

[starkindustries]

The OFF product schema carries per-100g nutriments AND per-serving info (serving_size as a label string, serving_quantity as the parsed gram weight). Per-100g nutriments are already indexed; per-serving siblings are not, so downstream consumers can't surface per-serving info via search-a-licious responses.

This adds both fields to the OFF index config:

• serving_size: type: text — user-contributed label string ("2 Tbsp (32 g)", "100g", "1 cup (240 ml)")
• serving_quantity: type: float — parsed grams per serving

Changes

• data/config/openfoodfacts.yml — two field entries adjacent to nutriments
• tests/int/data/test_off.yml + tests/unit/data/openfoodfacts_config.yml — matching entries in both test-schema files
• tests/int/test_search.py — adds serving values to one product in search_sample() and a new test_serving_fields test asserting both fields project through ES into the search response
• tests/unit/data/test_mapping.json — regenerated via pytest tests/unit/test_indexing.py --update-results

Local validation

• make test_api_unit → 42/42 pass
• make test_api_integration → 75 pass, 3 xfailed (vs. 73/3 baseline; +2 is the new test × GET/POST)

Question for reviewers

serving_quantity arrives from the OFF source doc as a string in many products but as a number in others. I picked type: float for parity with the per-100g nutriments. If you'd prefer text for consistency with serving_size, happy to switch.

Note

This is a schema-only addition. Existing OFF indexes won't have the new fields populated until reindexed.