- Implements robust WebDAV sync for servers without ETag support
- Adds _extractValidators method for ETag and Last-Modified headers
- Enhances conditional header creation with Last-Modified support
- Adds LOCK/UNLOCK mechanism for safe resource creation
- Implements server capability detection with caching
- Adds NoRevAPIError retry mechanism for missing validators
- Includes comprehensive test coverage for all workflows
- Maintains backward compatibility with existing ETag-based code
This enables WebDAV sync with basic servers that only support
Last-Modified headers while preserving optimal performance
for servers with full ETag support.
