v3 refactor (#1868)

* Move to v3

Co-authored-by: Ben Toogood <bentoogood@gmail.com>

client/mucp/mucp_request_test.go

@@ -0,0 +1,25 @@
+package mucp
+
+import (
+	"testing"
+
+	"github.com/micro/go-micro/v3/client"
+)
+
+func TestRequestOptions(t *testing.T) {
+	r := newRequest("service", "endpoint", nil, "application/json")
+	if r.Service() != "service" {
+		t.Fatalf("expected 'service' got %s", r.Service())
+	}
+	if r.Endpoint() != "endpoint" {
+		t.Fatalf("expected 'endpoint' got %s", r.Endpoint())
+	}
+	if r.ContentType() != "application/json" {
+		t.Fatalf("expected 'endpoint' got %s", r.ContentType())
+	}
+
+	r2 := newRequest("service", "endpoint", nil, "application/json", client.WithContentType("application/protobuf"))
+	if r2.ContentType() != "application/protobuf" {
+		t.Fatalf("expected 'endpoint' got %s", r2.ContentType())
+	}
+}