[Cosmos] [Embedding V0] Emulator tests + sample for embedding generation

[ananth7592]

Emulator tests + sample for embedding generation

Parent: 46729
Depends on: 46733, 46734, 46735

Goal

End-to-end smoke against the emulator (or a live Cosmos account once the gateway change ships) for a hybrid-search query that uses embedding_generator. Lives under sdk/cosmos/azure-cosmos/tests/ and sdk/cosmos/azure-cosmos/samples/.

Pre-requisite

This issue cannot be fully exercised end-to-end until the gateway change is live in either the emulator or a deployable backend, because Python has no serviceinterop fast path — it always asks the gateway for the query plan. The work itself can land behind the new feature flag (gated on embedding_generator being set) without breaking existing customers.

Scope

1. Extend tests/test_query_hybrid_search.py and tests/test_query_hybrid_search_async.py with at least one case that:
   • Issues a query expected to be rewritten with embeddingParameterMap.
   • Passes a mock generator that returns deterministic vectors (e.g. [float(i) for i in range(D)]).
   • Asserts the response is non-empty and the per-partition query was issued with the parameter populated. (One way: mock_send_request interception on the connection.)
   • Skips with a clear message when the gateway version doesn't yet support EmbeddingGeneration.
2. New sample under samples/:
   • embedding_generation_sample.py (sync)
   • embedding_generation_sample_async.py (async)
   • Shows how to implement an EmbeddingGenerator (a stub that returns [0.0] * 1536 is fine for the sample), and how to pass it to query_items.
3. CHANGELOG entry under the current unreleased version, calling out:
   • New EmbeddingGenerator / AsyncEmbeddingGenerator protocols.
   • New embedding_generator keyword on Container.query_items / ContainerProxy.query_items.
   • Dependency on the gateway change (link parent issue).

Files touched

• sdk/cosmos/azure-cosmos/tests/test_query_hybrid_search.py
• sdk/cosmos/azure-cosmos/tests/test_query_hybrid_search_async.py
• sdk/cosmos/azure-cosmos/samples/embedding_generation_sample.py (new)
• sdk/cosmos/azure-cosmos/samples/embedding_generation_sample_async.py (new)
• sdk/cosmos/azure-cosmos/CHANGELOG.md

Acceptance

• Emulator tests pass with a real or stubbed generator and document the gateway-version skip path.
• Samples run cleanly (or print "skipped: gateway support required" when not available).
• CHANGELOG entry is approved by the package's CODEOWNERS.