v3 refactor (#1868)

* Move to v3

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

server/mucp/rpc_util.go

@@ -0,0 +1,32 @@
+package mucp
+
+import (
+	"sync"
+)
+
+// waitgroup for global management of connections
+type waitGroup struct {
+	// local waitgroup
+	lg sync.WaitGroup
+	// global waitgroup
+	gg *sync.WaitGroup
+}
+
+func (w *waitGroup) Add(i int) {
+	w.lg.Add(i)
+	if w.gg != nil {
+		w.gg.Add(i)
+	}
+}
+
+func (w *waitGroup) Done() {
+	w.lg.Done()
+	if w.gg != nil {
+		w.gg.Done()
+	}
+}
+
+func (w *waitGroup) Wait() {
+	// only wait on local group
+	w.lg.Wait()
+}