fixed server only issues, properly separated client / server logic in common class.

src/main/java/carpet/mixins/ClientLevel_tickSpeedMixin.java

@@ -1,6 +1,6 @@
 package carpet.mixins;
 
-import carpet.fakes.ClientLevelInterface;
+import carpet.fakes.LevelInterface;
 import carpet.helpers.TickRateManager;
 import net.minecraft.client.multiplayer.ClientLevel;
 import org.spongepowered.asm.mixin.Mixin;
@@ -9,7 +9,7 @@ import org.spongepowered.asm.mixin.injection.Inject;
 import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
 
 @Mixin(ClientLevel.class)
-public class ClientLevel_tickSpeedMixin implements ClientLevelInterface
+public abstract class ClientLevel_tickSpeedMixin implements LevelInterface
 {
 
     private TickRateManager tickRateManager;
@@ -21,7 +21,7 @@ public class ClientLevel_tickSpeedMixin implements ClientLevelInterface
     }
 
     @Override
-    public TickRateManager getTickRateManager()
+    public TickRateManager tickRateManager()
     {
         return tickRateManager;
     }