docs: Update Claude provider comparison with deep-dive into vendors/claude source

- Added detailed analysis of 3419-line claude.ts implementation
- Expanded streaming comparison with 30+ features from original source
- Updated message conversion comparison with normalizeMessagesForAPI details
- Added comprehensive feature comparison table for streaming implementations
- Documented advanced features: idle watchdog, stall detection, VCR support,
  cache break detection, cost tracking, memory cleanup, request ID tracking