- Return Google's synchronous iterator directly from provider handler
- Detect Google streaming responses by checking for __iter__ but not __aiter__
- Convert Google chunks to OpenAI format in stream_generator
- Handle both sync (Google) and async (OpenAI/Anthropic) streaming responses
- Fix 'async_generator object is not iterable' error

This fixes streaming requests through autoselect and rotation handlers
that were failing with 'async_generator' object is not iterable error.