add claude caching

[teilomillet]

I have added Claude caching functionality with the following changes:

1. Added caching configuration options in settings.js:

   • Enable/disable caching via claudeOptions.cacheOptions.enabled
   • Configurable minimum tokens via claudeOptions.cacheOptions.minTokens

2. Modified ClaudeClient.js to support intelligent caching:

   • Added cache-specific headers in getHeaders()
   • Implemented strategic cache placement in buildApiParams():
     • Caches at branching points in conversations
     • Maintains last two branch points for efficient context switching
     • Uses remaining cache blocks for periodic checkpoints
     • Respects Claude's 4-block cache limit
   • Each cache block preserves full conversation context up to that point

3. Cache block distribution strategy:

   • System message (when present)
   • Two most recent conversation branch points
   • Periodic checkpoints every 10 messages (using remaining blocks)

4. Run 'npm audit fix' to fix vulnerabilities

Note: While the functionality is implemented following Anthropic's documentation, it requires testing to verify proper real-world performance, particularly around branch point detection and cache block distribution.

Testing needed:

• Branch point detection
• Cache block count limit
• Cache persistence (5-minute TTL)
• Performance impact on long conversations