bug: connects are created for every request

[judahrand]

Describe the bug

In both the GRPC and HTTP clients channels/sessions are created for every single request. Both GRPC and AIOHTTP recommend reusing channels/sessions for the lifecycle of the application.

• https://grpc.io/docs/guides/performance/#general
• https://docs.aiohttp.org/en/stable/client_reference.html#client-session

In both cases the channel/session encapsulates a connection pool. If a new channel/session is created for every request this connection pool must also be recreated. This leads to performance which is poorer than it could be.

Additionally, to really fix this problem each client needs to have its own implementation of _sync_call which is distinct from _call. Using asyncio.run in the background causes problems. It might be simpler and clearer to separate the clients into AsyncHTTPClient, HTTPClient, AsyncGrpcClient, and GrpcClient. Each of which could handle its simpler case.

To reproduce

No response

Expected behavior

Reuse of channels/sessions

Environment

N/A

[sauyon]

HTTP resolved in #4116; we should probably consider gRPC at some point.