Fail on duplicate simple types

src/main/java/org/quiltmc/enigma_plugin/index/simple_type_single/SimpleTypeFieldNamesRegistry.java

@@ -57,6 +57,10 @@ public void read() {
 			while (reader.hasNext()) {
 				String type = reader.nextName();
 
+				if (this.entries.containsKey(type)) {
+					throw new IllegalArgumentException("Duplicate type " + type);
+				}
+
 				switch (reader.peek()) {
 					case STRING -> {
 						String localName = reader.nextString();