* devops: Variable product performance optimization and tests
- Memoize get_variation_prices() in the Product model to avoid
redundant lookups across multiple pricing fields (price, regularPrice,
salePrice, and their RAW variants)
- Remove redundant post__in filter from variations connection resolver;
post_parent already constrains the query, and the post__in triggered
an extra get_children() call per product
- Add createVariableProductCatalog() helper to GraphQLE2E for creating
variable products with many variations in tests
- Add VariableProductPerformanceTest (wpunit) measuring DB query count
and duration for 15 variable products with 18 variations each
- Add VariableProductPerformanceCest (functional) verifying 6 rapid
queries do not return 429 errors
Addresses #897
* fix: Skip timing assertion when xdebug is active and clean up debug code
