Add Nullable annotation to RecipeMap::getByName()

IDE analysis assumes it won't return null otherwise, because methods
are marked Non-null by default.

src/main/java/gregtech/api/recipes/RecipeMap.java

@@ -100,6 +100,7 @@ public static List<RecipeMap<?>> getRecipeMaps() {
     }
 
     @ZenMethod
+    @Nullable
     public static RecipeMap<?> getByName(String unlocalizedName) {
         return RECIPE_MAPS.stream()
             .filter(map -> map.unlocalizedName.equals(unlocalizedName))