multi: prepare for new non-constant string rule

In preparation for the next commit which bumps golang to a newer
version, we want to make some code changes that would otherwise render
some log-related calls problematic. With go1.24 a new govet rule was
added that disallows non-constant strings (i.e including a tag like
"%s") in calls to printf. See more in the related issue
https://github.com/golang/go/issues/60529.

itest/network_harness.go

@@ -270,12 +270,10 @@ out:
 
 	n.EnsureConnected(t, n.Alice, n.Bob)
 
-	logLine := fmt.Sprintf(
-		"STARTING ============ %v ============\n", testCase,
-	)
+	logLine := "STARTING ============ %v ============\n"
 
-	n.Alice.AddToLog(logLine)
-	n.Bob.AddToLog(logLine)
+	n.Alice.AddToLog(logLine, testCase)
+	n.Bob.AddToLog(logLine, testCase)
 
 	return nil
 }

rpc_proxy.go

@@ -364,7 +364,7 @@ func (p *rpcProxy) makeDirector(allowLitRPC bool) func(ctx context.Context,
 		// gRPC server.
 		handled, conn, err := p.subServerMgr.GetRemoteConn(requestURI)
 		if err != nil {
-			return outCtx, nil, status.Errorf(
+			return outCtx, nil, status.Error(
 				codes.Unavailable, err.Error(),
 			)
 		}

rpcmiddleware/proto.go

@@ -76,8 +76,12 @@ func RPCErrString(req *lnrpc.RPCMiddlewareRequest, format string,
 		},
 	}
 
+	if len(args) > 0 {
+		format = fmt.Sprintf(format, args...)
+	}
+
 	if format != "" {
-		feedback.Error = fmt.Sprintf(format, args...)
+		feedback.Error = format
 	}
 
 	return resp, nil

status/manager.go

@@ -264,18 +264,20 @@ func (s *Manager) SetErrored(name string, errStr string,
 	s.mu.Lock()
 	defer s.mu.Unlock()
 
-	err := fmt.Sprintf(errStr, params...)
+	if len(params) > 0 {
+		errStr = fmt.Sprintf(errStr, params...)
+	}
 
-	log.Debugf("Setting the %s sub-server as errored: %s", name, err)
+	log.Debugf("Setting the %s sub-server as errored: %s", name, errStr)
 
 	ss, ok := s.subServers[name]
 	if !ok {
 		return
 	}
 
-	log.Errorf("could not start the %s sub-server: %s", name, err)
+	log.Errorf("could not start the %s sub-server: %s", name, errStr)
 
 	ss.running = false
-	ss.err = err
+	ss.err = errStr
 	ss.customStatus = ""
 }

terminal.go

@@ -431,10 +431,7 @@ func (g *LightningTerminal) start(ctx context.Context) error {
 	var err error
 
 	accountServiceErrCallback := func(err error) {
-		g.statusMgr.SetErrored(
-			subservers.ACCOUNTS,
-			err.Error(),
-		)
+		g.statusMgr.SetErrored(subservers.ACCOUNTS, err.Error())
 
 		log.Errorf("Error thrown in the accounts service, keeping "+
 			"litd running: %v", err,