Add multiplex support

[MATATAT]

Hello! I've been using mocktail for a recent project and decided on it because I need both mocking for http as well as grpc. Currently the project does support "multiplexing" if you just choose .new_http() since the only thing barring http and grpc from cohabitating is a check for http2 explicitly if using .new_grpc().

If this is something that y'all are interested in I can take a stab at it and create a PR.

[declark1]

Just to clarify, what do you mean by adding multiplex support? I understand this is an HTTP/2 feature and the MockServer already supports both HTTP/1 and HTTP/2 connections via hyper_util::server::conn::auto::Builder. Since gRPC is HTTP/2 only, I set it to only accept HTTP/2 for this service.

[mattmacdonald-m42]

Yeah sorry I think I have my terminology wrong. I just mean supporting both, which does happen, but it’s a little confusing to choose HTTP to support both formats.

Maybe even some doc comments would help make it clearer.