added perf command support

src/main/java/carpet/mixins/PerfCommand_permissionMixin.java

@@ -0,0 +1,21 @@
+package carpet.mixins;
+
+import carpet.CarpetSettings;
+import net.minecraft.server.command.ServerCommandSource;
+import net.minecraft.server.dedicated.command.PerfCommand;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+
+@Mixin(PerfCommand.class)
+public class PerfCommand_permissionMixin
+{
+    @SuppressWarnings("UnresolvedMixinReference")
+    @Inject(method = "method_37340(Lnet/minecraft/server/command/ServerCommandSource;)Z", at = @At("HEAD"), cancellable = true)
+    private static void canRun(ServerCommandSource source, CallbackInfoReturnable<Boolean> cir)
+    {
+        cir.setReturnValue(source.hasPermissionLevel(CarpetSettings.perfPermissionLevel));
+    }
+
+}