Add comprehensive support for Claude's extended thinking feature in Kiro provider:
- Add thinking block parsing and streaming with proper tag detection
- Implement thinking prefix injection in system prompts with budget validation
- Add bidirectional conversion between Kiro text format and Claude content blocks
- Enhance token estimation with detailed breakdown for thinking, tools, and content types
- Fix streaming to properly handle thinking blocks with start/stop events
- Improve context usage percentage handling and input token calculation
- Add helper functions for quote-aware tag detection to avoid false positives