when batch is true in DelegateInputHandler, filter simultaneous keydown/keyup

thermion_dart/lib/src/input/src/delegate_input_handler.dart

@@ -60,12 +60,15 @@ class DelegateInputHandler implements InputHandler {
       ]);
 
   Future<void> process() async {
-    
     _processing = true;
 
     final delegate = delegates.first;
-    final keyUp = <LogicalKey, KeyEvent>{};
-    final keyDown = <LogicalKey, KeyEvent>{};
+
+    late final Map<LogicalKey, KeyEvent> keyDown;
+    // if batch is true, we treat any tick containing keydown/keyup for the same key as a keydown
+    if (batch) {
+      late final Map<LogicalKey, KeyEvent> keyUp = {};
+      keyDown = {};
 
       for (final event in _events) {
         if (event is KeyEvent) {
@@ -81,11 +84,14 @@ class DelegateInputHandler implements InputHandler {
         _events.remove(keyDown[key]);
         _events.remove(keyUp[key]);
       }
+    }
 
     await delegate.handle(_events.sublist(0));
-
     _events.clear();
+    if (batch) {
       _events.addAll(keyDown.values);
+    }
+
     _processing = false;
   }