v0.20.0: Connection persistence with offer rotation

Implement connection persistence for offerer side through "offer rotation".
When a connection fails, the same OffererConnection object is rebound to a
new offer instead of being destroyed, preserving message buffers and event
listeners.

Features:
- Connection objects persist across disconnections
- Message buffering works seamlessly through rotations
- Event listeners remain active after rotation
- New `connection:rotated` event for tracking offer changes
- Max rotation attempts limit (default: 5) with fallback

Implementation:
- Add OffererConnection.rebindToOffer() method with AsyncLock protection
- Add rotation tracking: rotating flag, rotationAttempts counter
- Add OfferPool.createNewOfferForRotation() helper method
- Modify OfferPool failure handler to rotate instead of destroy
- Add connection:rotated event to OfferPoolEvents interface
- Forward connection:rotated event in Rondevu class
- Add edge case handling for cleanup during rotation
- Reset rotation attempts on successful connection

Documentation:
- Add "Connection Persistence" section to README with examples
- Update "New in v0.20.0" feature list
- Add v0.20.0 changelog entry
- Document rotation benefits and behavior

Benefits:
- Same connection object remains usable through disconnections
- Message buffer preserved during temporary disconnections
- Event listeners don't need to be re-registered
- Simpler user code - no need to track new connections

100% backward compatible - no breaking changes.

🤖 Generated with Claude Code (https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@xtr-dev/rondevu-client",
-  "version": "0.19.0",
+  "version": "0.20.0",
   "description": "TypeScript client for Rondevu with durable WebRTC connections, automatic reconnection, and message queuing",
   "type": "module",
   "main": "dist/index.js",