[Cosmos] [Embedding V0] Public surface: EmbeddingGenerator protocols + embedding_generator on query_items

[ananth7592]

Public surface: EmbeddingGenerator protocols + embedding_generator keyword on query_items

Parent: 46729

Goal

Add the customer-facing API for embedding generation, with no behavioral change yet.

Scope

1. New protocols (export from package root, e.g. azure.cosmos):

   from typing import Protocol, Sequence
   
   @runtime_checkable
   class EmbeddingGenerator(Protocol):
       def generate_embeddings(self, texts: Sequence[str]) -> Sequence[Sequence[float]]: ...
   
   @runtime_checkable
   class AsyncEmbeddingGenerator(Protocol):
       async def generate_embeddings_async(self, texts: Sequence[str]) -> Sequence[Sequence[float]]: ...

2. New keyword-only argument on query_items:
   • azure/cosmos/container.py :: Container.query_items – embedding_generator: Optional["EmbeddingGenerator"] = None
   • azure/cosmos/aio/_container.py :: ContainerProxy.query_items – embedding_generator: Optional["AsyncEmbeddingGenerator"] = None
3. Stuff into feed_options:

   if embedding_generator is not None:
       feed_options["embeddingGenerator"] = embedding_generator

   Mirror the existing pattern at container.py:1055-1058 (full_text_score_scope).
4. Type hints + docstrings (Sphinx). Add to _overloads typing files if present.

Non-goals

• Do NOT yet read the option in any execution path (will be added in 46733).
• Do NOT yet add the _QueryFeature token (covered by 46731).
• Do NOT add a built-in implementation. The EGS package owns that.

Files touched

• sdk/cosmos/azure-cosmos/azure/cosmos/__init__.py (export new protocols)
• sdk/cosmos/azure-cosmos/azure/cosmos/container.py
• sdk/cosmos/azure-cosmos/azure/cosmos/aio/_container.py
• New: sdk/cosmos/azure-cosmos/azure/cosmos/_embedding_generator.py (or in documents.py)
• sdk/cosmos/azure-cosmos/CHANGELOG.md

Acceptance

• from azure.cosmos import EmbeddingGenerator, AsyncEmbeddingGenerator works.
• query_items(..., embedding_generator=mock) is accepted and stored without error.
• Mypy / pyright pass on the new protocols.
• Existing query_items callers unchanged.