Improve StringByteString performance

luna/src/main/java/org/classdump/luna/StringByteString.java

@@ -64,6 +64,10 @@ class StringByteString extends ByteString {
       return true;
     }
 
+    if (that instanceof StringByteString tstring) {
+      return string.equals(tstring.string);
+    }
+
     // don't force hashCode computation, but use if already known
     int thisHash = this.maybeHashCode();
     int thatHash = that.maybeHashCode();

src/main/kotlin/ru/dbotthepony/kstarbound/lua/Conversions.kt

@@ -230,9 +230,11 @@ private object JsonTableIndex : AbstractFunction3<Table, Any, Any?>() {
 		throw NonsuspendableFunctionException(this::class.java)
 	}
 
+	private val __nils: ByteString = ByteString.of("__nils")
+
 	override fun invoke(context: ExecutionContext, self: Table, key: Any, value: Any?) {
 		val meta = self.metatable
-		val nils = meta["__nils"] as Table
+		val nils = meta[__nils] as Table
 
 		// If we are setting an entry to nil, need to add a bogus integer entry
 		// to the __nils table, otherwise need to set the entry *in* the __nils