Add multi-part request messages

Makefile

go.mod

go.sum

single/cypher.go

single/listener.go

single/message/collator.go

single/message/collator_test.go

single/message/request.go

single/message/requestPart.go

single/message/requestPart_test.go

single/receivedRequest.go

single/request.go

single/requestPartProcessor.go

single/responseProcessor.go

single/roundCollector.go