⚡ perf: index review summaries by entity_id for O(1) lookup

[lbajsarowicz]

Summary

• Replace O(n²) nested foreach in Review::appendSummary() with pre-indexed associative array for O(n) total complexity.
• Summaries are indexed by entity_pk_value before the product loop, then looked up via isset() instead of scanning all summaries per product.
• Behavior is identical: matching products get the summary, non-matching products get an empty DataObject.

Performance Impact

Metric	Before	After
Complexity	O(n × m) nested foreach	O(n + m) with indexed lookup
100 products × 100 summaries	10,000 comparisons	200 iterations

Test Plan

• Unit test with DataProvider covering:
  • Products with matching summaries
  • Products with no matching summary (empty DataObject fallback)
  • Empty summary collection
• PHPCS clean (requires CI)
• PHPStan clean (requires CI)

Ref: #40717

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[lbajsarowicz]

@magento run all tests