Use nim-async-channels to communicate threads

[Ivansete-status]

The communication between the working/FFI and client thread happens throughout taskpools/channels_spsc_single. While this works well in general, the client thread might get eventually blocked in the following, if the working thread is busy:

nim-ffi/ffi/ffi_context.nim

Line 73 in 803744d

let res = ctx.reqReceivedSignal.waitSync(timeout)

Then, we need to follow @arnetheduck's suggestion and, instead, use this: https://github.com/status-im/nim-async-channels

Note: use the following as an inspiration on how to use it: status-im/nim-json-rpc#254

( cc @NagyZoltanPeter .)

[NagyZoltanPeter]

My view on using AsyncChannels:

• it is convenient to use but with tradeoffs
• without this PR merged (or similar solution) improve asyncchannel usage and thread safety guarantees status-im/nim-async-channels#3 it is wiser to intentionally leak the allocated channel as there is no way to safely - threadwise - deallocated the resources. In other words in-flight messages can cause crash.
• AsyncChannels - depending on the design/usage - can lead to resource limits (depending on platform also).
  • in MacOS the default max-files for a process, terminal session is only 256. My nim-brokers ran into this limit with testing many different requests and events on multiple threads caused resource allocation issue. One AsyncChannel needs to FD handles.

cc: @arnetheduck

[fcecin]

Moving to Icebox because the suggested solution consumes too many resources (at least on MacOS).

[Ivansete-status]

Closing for now. We'll reopen in the future, if needed. Thanks