Python: Embedding clients have no close()/context manager and leak their internally created SDK clients #9814

Description

#9748 added deterministic lifecycle to chat clients (async with, close(), connector-owned resource release), but the embedding client family was left out:

• BaseEmbeddingClient has no __aenter__/__aexit__/close(), so async with does not work for any embedding client, and there is no contract for releasing resources.
• OpenAIEmbeddingClient creates an AsyncOpenAI/AsyncAzureOpenAI SDK client internally (owning an httpx connection pool) when async_client is not supplied, and offers no way to close it — only GC ever releases the pool.
• BedrockEmbeddingClient creates a boto3 bedrock-runtime client internally with the same gap.
• OllamaEmbeddingClient creates an AsyncClient (httpx transport) internally with the same gap.
• GeminiEmbeddingClient already implements close() with _owns_client — the rest of the family is inconsistent with it and with the chat clients.

Repro

from agent_framework_openai import OpenAIEmbeddingClient

client = OpenAIEmbeddingClient(api_key="...")
async with client:  # TypeError: 'async with' received an object that does not implement __aenter__
    ...
# and the internally created AsyncOpenAI is never closed deterministically

Long-lived processes that build embedding clients per unit of work (e.g. per request/tenant) accumulate unclosed httpx pools until GC runs, which is exactly the class of leak #9748 fixed for chat clients.

Expected

Embedding clients follow the same contract #9748 established for chat clients: base-class context trio with a no-op default close(), and resource-owning implementations that close only the SDK client they created (caller-supplied clients stay open), idempotent on repeated close.

Environment

• Packages: agent-framework-core, agent-framework-openai, agent-framework-bedrock, agent-framework-ollama
• Observed on main at 4a272d2 (i.e. including Python: Add async context managers to chat clients #9748)