- Introduced `SystemInstruction` field in `PrepareRequest` and `GenerateContentRequest` for better message parsing.
- Updated `SendMessage` and `SendMessageStream` to handle system instructions in client API calls.
- Enhanced error handling and manual flushing logic in response flows.
- Added new internal API endpoints `/v1internal:generateContent` and `/v1internal:streamGenerateContent`.
- Improved proxy handling and transport logic in HTTP client initialization.
- Introduced `QuotaExceeded` settings in configuration to handle quota limits more effectively.
- Added preview model switching logic to `Client` to automatically use fallback models on quota exhaustion.
- Refactored `APIHandlers` to leverage new configuration structure.
- Simplified server initialization and removed redundant `ServerConfig` structure.
- Streamlined client initialization by unifying configuration handling throughout the project.
- Improved error handling and response mechanisms in both streaming and non-streaming flows.
