* fix: ChatGPT import logic breaks message graph when it encounters a system message
- Implemented `findNonSystemParent` to maintain parent-child relationships by skipping system messages.
- Added a test case to ensure system messages do not disrupt the conversation flow during import.
* fix: ChatGPT import, correct sender for user messages with GPT-4 model
* fix: Enhance model name extraction for assistant messages in import process
- Updated sender assignment logic to dynamically extract model names from model slugs, improving accuracy for various GPT models.
- Added comprehensive tests to validate the extraction and formatting of model names from different model slugs, ensuring robustness in the import functionality.