ReqResp encoded bytes API

[dapplion]

• Issue feat: move libp2p to network worker thread #5229 would benefit greatly from ReqResp dealing with non deserialized SSZ data structures

Since ReqResp requests and responses must cross the worker boundary it's best to just wait to de-serialize them on the main thread. For it the API exposed by the reqresp package must deal exclusively with Uint8Array instead of T representing the deserialized object. For reference of how the API should look like PR #5229 is quasi complete reference.

[nazarhussain]

Based on discussion with @wemeetagain came up with this diagram to align the understanding for everyone.