Detach live websocket wrappers from a dead RequestServer connection,
notify them with error and close events, and defer the
on_request_server_died callback out of RequestClient::die().
Without this, a dead RequestServer could leave existing websocket
objects stuck forever and future websocket construction could keep
using a stale RequestClient with no terminal events.
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.
