Add Product API Structure Validation tests. See TEST003

[VivanReddy13]

Ticket

• TEST003

Description

Created test/test_003_product_api_structure.py with 18 tests validating
the Product Detail API response structure.

Tests cover:

• Required fields present (barcode, productName)
• All contract fields present and correctly named
• Data types are correct (strings, arrays, dicts, numbers)
• nutriments_normalized contains all expected keys
• Missing values handled safely with empty lists and None
• Frontend rendering safety — no crashes on minimal product
• enrichmentMetadata mapped correctly
• nutriscoreGrade is a valid value
• completeness is between 0 and 1

Result: 18/18 tests passed.

Checks

• [ x] All requirements of the ticket have been implemented, or I have commented on any exclusions
• [ x] Unit tests have been added or updated for any backend changes (if applicable)
• [ x] I have reviewed the Files Changed tab and verified it only contains relevant changes (comment if unsure about any)
• This PR has been reviewed and approved

Screenshots