Websocket RPC pitfalls

[hobofan]

12 added the websocket RPC, but there are some caveats with it:

• Only one subscription per connection right now. Not sure how much impact that actually has with most clients, but should be resolved sooner or later.
• Doubt if the way we consume the stream is the proper way to do it: https://github.com/rlay-project/rlay-client/blob/93b7670decf015c7304868bae4ad6e472759405a/src/rpc/mod.rs#L96 For now it works well enough as it consumes all outstanding entities as fast as it can, but it introduces a delay of up to 100ms for any incoming entities

[hobofan]

• I think the websocket future streams also don't finish correctly when a websocket connection is closed.