Add caching layer to improve performance when repeatedly accessing
the same OpenAPI specs:
- LRU cache with max 10 entries and 15-minute TTL
- Cache key includes mtime for local files (change detection)
- URL normalization for consistent remote spec caching
- noCache parameter on all tools to bypass cache
- Response includes cached:true/false indicator
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
