fix(autogen-ext): preserve Azure model info in component config

[YZJF,YCDG,DJLY,ZZZB (YZJF)]

Why are these changes needed?

Before this change, AzureOpenAIChatCompletionClient removed model_info and
the deprecated model_capabilities from the SDK arguments before saving
_raw_config. As a result, dump_component() omitted the model capabilities required
to load a custom Azure deployment whose name is not in AutoGen's built-in model
table.

Save the original constructor configuration for component serialization, while
continuing to pass the filtered arguments to the Azure SDK. This mirrors the
existing OpenAIChatCompletionClient behavior introduced in #5315.

The regression test uses a fake endpoint and key, serializes an unknown Azure
deployment to JSON, then loads it back and verifies that model_info is
preserved. It makes no network model call.

Related issue number

N/A — this is an Azure parity gap discovered while auditing component
serialization; no matching open issue or PR was found.

Checks

• No documentation update is needed; this restores the documented component configuration round-trip behavior.
• I've added a regression test corresponding to the fix.
• GitHub automated checks have not run yet.

Local validation

• uv run --no-sync pytest packages/autogen-ext/tests/models/test_openai_model_client.py -k azure_openai_chat_completion_client_serializes_model_info -q (1 passed)
• uv run --no-sync pytest packages/autogen-ext/tests/models/test_openai_model_client.py -q (54 passed, 33 skipped)
• uv run --no-sync ruff format --check packages/autogen-ext/src/autogen_ext/models/openai/_openai_client.py packages/autogen-ext/tests/models/test_openai_model_client.py
• uv run --no-sync ruff check packages/autogen-ext/src/autogen_ext/models/openai/_openai_client.py packages/autogen-ext/tests/models/test_openai_model_client.py
• Scoped MyPy and Pyright checks on the changed source and test files (both passed)

I also attempted the full autogen-ext MyPy command; this dependency subset reports existing missing-optional-integration type errors in unrelated Semantic Kernel, Ollama, and llama-cpp files, not in the changed files.

AI assistance

This change and regression test were prepared with AI assistance. The local validation commands above were run against this branch.