fix(kcp): enable congestion control, add FEC, and fix remote node UDP diagnosis

- KCP: switch from fast3 to fast2 mode, enable FEC (10/3), enable
  congestion control (nc=0) for automatic rate adaptation
- go-gost/x: support kcp.nc metadata to override mode-initialized
  NoCongestion value in dialer and listener Init()
- Diagnosis: add udpPingViaRemoteNode, fix pingViaRemoteNode to
  dispatch based on protocol, add Protocol field to federation
  diagnose request structs

go-backend/internal/http/client/federation.go

@@ -71,10 +71,11 @@ type RuntimeReleaseRoleRequest struct {
 }
 
 type RuntimeDiagnoseRequest struct {
-	IP      string `json:"ip"`
-	Port    int    `json:"port"`
-	Count   int    `json:"count"`
-	Timeout int    `json:"timeout"`
+	IP       string `json:"ip"`
+	Port     int    `json:"port"`
+	Count    int    `json:"count"`
+	Timeout  int    `json:"timeout"`
+	Protocol string `json:"protocol"`
 }
 
 type RuntimeNodeCommandRequest struct {