Analysis of debug.log showed 429 rate limit errors during streaming
were not being caught by the retry logic because:
1. Streaming generators don't raise exceptions until consumed
2. Error message 'Claude API error (429): Error' didn't contain retry keywords

Changes:
1. Added _handle_streaming_request_with_retry() wrapper that catches
   rate limit errors and re-raises with proper keywords
2. Added _wrap_streaming_with_retry() method that consumes streaming
   generator and retries with fallback models on rate limit errors
3. Updated retry logic to check for '429' keyword in error messages
4. Added exponential backoff with jitter before retry attempts
5. Improved error messages to include rate limit context

This ensures that when streaming hits a 429 rate limit, the system
will automatically retry with fallback models instead of failing.