Added four new exception classes to improve error handling:
- DatabaseConnectionError: Enhanced database connection errors with recovery hints
- DatabaseTimeoutError: Timeout errors with operation context
- EncodingError: UTF-8 and character encoding issues
- DataValidationError: Data validation failures in RAG processing
These exceptions provide better error messages, contextual information, and recovery suggestions for common database and encoding issues reported in the issues tracker.
- Add StorageNotInitializedError and PipelineNotInitializedError exceptions
- Update JsonDocStatusStorage to raise clear errors when not initialized
- Update JsonKVStorage to raise clear errors when not initialized
- Error messages now include complete initialization instructions
- Helps users understand and fix initialization issues quickly
Addresses feedback from issue #1933 about improving error clarity
