Fix more warnings and do some small optimizations (#1356)

* Fix more warnings and do some small optimizations

* Fix more warnings in ValueConversions

* Clean up some decompiler names and fix an unnecessary transformation around commands

* Use (way) more compact data structure for slot map

* Minor tweaks
Such as map directly in the collector

* I hate vanilla javac
Revert map changes in latest commit

src/main/java/carpet/script/value/NBTSerializableValue.java

@@ -516,7 +516,7 @@ public class NBTSerializableValue extends Value implements ContainerValueInterfa
             }
             try
             {
-                CollectionTag<?> targetList = (CollectionTag) target;
+                CollectionTag<?> targetList = (CollectionTag<?>) target;
                 if (!targetList.addTag(index < 0 ? targetList.size() + index + 1 : index, newElement.copy()))
                     return false;
                 modified = true;