feat: changed ObjectMapper to static for the JSON deserializers

src/main/java/uulm/teamname/marvelous/gamelibrary/json/ingame/EntityDeserializer.java

@@ -21,7 +21,8 @@ public class EntityDeserializer extends JsonDeserializer<Entity> {
         Rock
     }
 
-    private final ObjectMapper mapper = new ObjectMapper();
+    // static so that no reinitializations are needed
+    private static final ObjectMapper mapper = new ObjectMapper();
 
     @Override
     public Entity deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {

src/main/java/uulm/teamname/marvelous/gamelibrary/json/ingame/EventDeserializer.java

@@ -22,7 +22,8 @@ import java.util.HashMap;
 
 public class EventDeserializer extends JsonDeserializer<Event> {
 
-    private final ObjectMapper mapper = new ObjectMapper();
+    // static so that no reinitializations are needed
+    private static final ObjectMapper mapper = new ObjectMapper();
 
     @Override
     public Event deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {

src/main/java/uulm/teamname/marvelous/gamelibrary/json/ingame/IntVector2Deserializer.java

@@ -13,7 +13,8 @@ import java.io.IOException;
 
 public class IntVector2Deserializer extends JsonDeserializer<IntVector2> {
 
-    ObjectMapper mapper = new ObjectMapper();
+    // static so that no reinitializations are needed
+    private static final ObjectMapper mapper = new ObjectMapper();
 
     @Override
     public IntVector2 deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {