Transform Pydantic output config formats

[uuzzrm]

Fixes #1819.

output_config.format now accepts the same Pydantic model input that the deprecated output_format parameter accepted, and sends model-generated schemas through the existing transform_schema path before request serialization. Raw JSON schema dictionaries remain unchanged and continue to be sent as provided.

The conversion is applied consistently to the stable and beta Messages APIs for synchronous and asynchronous create, parse, stream, and count_tokens calls. The public OutputConfigParam types now include Pydantic model classes.

The change is intentionally scoped to the Messages API surfaces covered by this issue; Message Batches and refusal fallbacks are unchanged.

Tests

• uv run pytest tests/lib/_parse/test_transform.py tests/api_resources/test_output_config_format_conversion.py -q — 32 passed, 1 skipped
• Ruff checks and format checks passed for all changed files
• git diff --check passed

The repository test wrapper could not start its mock server on this machine because Node is missing libllhttp.9.3.dylib; the targeted tests ran without that wrapper.

AI assistance was used for implementation and validation. The final diff was checked against the issue and the targeted test results before this update.