MAGE-1329 integration tests

[cammonro]

Summary
This PR introduces an integration testing suite to the backend adapter module utilizing the core module integration test classes and helpers.

• Base Test Case - Provides reusable infrastructure:
  • Methods for building filters (category, price, attribute)
  • Assertion helpers for documents, facets, and sorting
• Test Coverage:
  • Basic search results verification
  • Facet aggregations (category, price, color, size)
  • Category/price/attribute filtering
  • Multiple filters combined
  • Pagination across pages
  • Price and name sorting (ascending/descending)
  • Routing configuration for Magento vs Algolia parameter modes
  • Replica sync when backend search is enabled without InstantSearch
  • All of these search tests can run with the OpenSearch / ElasticSearch server disabled
• Configuration Fixtures - Tests use @magentoConfigFixture annotations to:
  • Set catalog/search/engine = algolia
  • Disable InstantSearch for backend-only testing
  • Configure query string parameter mode
• Category cache testing
  • This ports the test from the original implementation in support of the new backend render delivered on MAGE-1325 backend render with InstantSearch for bots #21
  • More work can be done here to completely decouple from OpenSearch / ElasticSearch - for now OpenSearch must be running for the test to succeed

The tests are designed to index products to Algolia, execute searches via the Adapter::query() method, and verify that results match expectations for backend search parity.

Note

Please note this that PR depends on changes introduced in algolia/algoliasearch-magento-2#1903

Result