fix(memory): improve content parsing in retrieveContext

- Add proper handling of role-prefixed content
- Special handling for system messages
- Skip empty content to avoid errors
- Maintain role information for non-system messages
- Improve documentation with supported message formats

refactor(memory): align ChromeDB document structure

- Update StoreMemory to match ChromeDB's document requirements
- Move timestamp and collection into metadata map
- Add roles tracking in metadata
- Enhance documentation with detailed structure and processing steps

fix: improve collection management for memory sharing

This commit improves how collections are managed in SimpleRAG and Register:

1. Remove collection drop on SimpleRAG initialization
2. Add proper collection creation with schema
3. Ensure collections are loaded before processing
4. Improve error handling and logging

These changes fix the 'Inserting 0 records' issue and enable
proper memory sharing between different instances.

feat(retriever): smart handling of empty collections and TopK adjustment

- Add two-step search process to verify collection contents
- Implement dynamic TopK adjustment based on available documents
- Add informative logging for various retrieval scenarios
- Gracefully handle cases where requested TopK exceeds available documents

refactor: fix formatting and update ChromemDB reference in comments

Update the embedder references

add some comments

update the readme