- Added an example plugin `host-model-callback` in Go to summarize host model callbacks. - Implemented `cliproxy_plugin_init`, `cliproxyPluginCall`, and other plugin functions for callback handling. - Introduced API handlers for `ModelExecution` and `ModelExecutionStream` with support for both streaming and non-streaming requests. - Included unit tests (`model_execution_test.go`) to validate execution logic and streaming responses.