ag-ui 是做什么的？
Add or modify a wire transport / event-stream encoding in the AG-UI .NET SDK — the protobuf codec, the SSE format, content negotiation, the JsonElement-to-protobuf Value bridge, or a brand new encoding — while preserving Native AOT compatibility and byte-level wire compatibility with @ag-ui/proto. USE FOR: working on AGUI.Formatting / AGUI.Protobuf, IAGUIEventStreamFormatter, transport content negotiation, the JsonElement-to-google.protobuf.Value bridge, SSE or protobuf framing, server formatter