The bug fixed here is that in RequestServer's ConnectionFromClient, we
stored the websocket ID as i32, despite it being i64 everywhere else.
Let's make it unsigned while we are here to be consistent with how all
other RS-related IDs will be soon.
We used to need an allocated ByteBuffer to send over IPC. Our IPC now
accepts spans for types like String and ByteBuffer though, so we don't
need to allocate buffers at the caller.
