[client] Add unit tests for engine synchronization and Info flag copying

- Introduced tests for the Engine's handleSync method to verify behavior when SkipNetworkMapUpdate is true and when NetworkMap is nil.
- Added a test for the Info struct to ensure correct copying of flag values from one instance to another, while preserving unrelated fields.

client/system/info_test.go

@@ -1,13 +1,72 @@
 package system
 
 import (
-	"context"
-	"testing"
+    "context"
+    "testing"
 
-	"github.com/stretchr/testify/assert"
-	"google.golang.org/grpc/metadata"
+    "github.com/stretchr/testify/assert"
+    "google.golang.org/grpc/metadata"
 )
 
+func TestInfo_CopyFlagsFrom(t *testing.T) {
+	origin := &Info{}
+	serverSSHAllowed := true
+	origin.SetFlags(
+		true,   // RosenpassEnabled
+		false,  // RosenpassPermissive
+		&serverSSHAllowed,
+		true,  // DisableClientRoutes
+		false, // DisableServerRoutes
+		true,  // DisableDNS
+		false, // DisableFirewall
+		true,  // BlockLANAccess
+		false, // BlockInbound
+		true,  // LazyConnectionEnabled
+	)
+
+	got := &Info{}
+	got.CopyFlagsFrom(origin)
+
+	if got.RosenpassEnabled != true {
+		t.Fatalf("RosenpassEnabled not copied: got %v", got.RosenpassEnabled)
+	}
+	if got.RosenpassPermissive != false {
+		t.Fatalf("RosenpassPermissive not copied: got %v", got.RosenpassPermissive)
+	}
+	if got.ServerSSHAllowed != true {
+		t.Fatalf("ServerSSHAllowed not copied: got %v", got.ServerSSHAllowed)
+	}
+	if got.DisableClientRoutes != true {
+		t.Fatalf("DisableClientRoutes not copied: got %v", got.DisableClientRoutes)
+	}
+	if got.DisableServerRoutes != false {
+		t.Fatalf("DisableServerRoutes not copied: got %v", got.DisableServerRoutes)
+	}
+	if got.DisableDNS != true {
+		t.Fatalf("DisableDNS not copied: got %v", got.DisableDNS)
+	}
+	if got.DisableFirewall != false {
+		t.Fatalf("DisableFirewall not copied: got %v", got.DisableFirewall)
+	}
+	if got.BlockLANAccess != true {
+		t.Fatalf("BlockLANAccess not copied: got %v", got.BlockLANAccess)
+	}
+	if got.BlockInbound != false {
+		t.Fatalf("BlockInbound not copied: got %v", got.BlockInbound)
+	}
+	if got.LazyConnectionEnabled != true {
+		t.Fatalf("LazyConnectionEnabled not copied: got %v", got.LazyConnectionEnabled)
+	}
+
+	// ensure CopyFlagsFrom does not touch unrelated fields
+	origin.Hostname = "host-a"
+	got.Hostname = "host-b"
+	got.CopyFlagsFrom(origin)
+	if got.Hostname != "host-b" {
+		t.Fatalf("CopyFlagsFrom should not overwrite non-flag fields, got Hostname=%q", got.Hostname)
+	}
+}
+
 func Test_LocalWTVersion(t *testing.T) {
 	got := GetInfo(context.TODO())
 	want := "development"