Prepare the v0.4.3 beta release with major feature additions and improvements:
- Add JsonXPathExtractionStrategy and LLMContentFilter to exports
- Update version to 0.4.3b1
- Improve documentation for dispatchers and markdown generation
- Update development status to Beta
- Reorganize changelog format
BREAKING CHANGE: Memory threshold in MemoryAdaptiveDispatcher increased to 90% and SemaphoreDispatcher parameter renamed to max_session_permit
