audio display: limit mouse event rate

Same as with visual typesetting.

src/audio_display.cpp

@@ -1045,6 +1045,13 @@ void AudioDisplay::OnMouseLeave(wxMouseEvent&)
 
 void AudioDisplay::OnMouseEvent(wxMouseEvent& event)
 {
+	// wx doesn’t throttle for us, updating the video view is
+	// very expensive, and aegisub’s work queue handling is bad,
+	// so limit mouse event rate to ~200 Hz
+	long ts = event.GetTimestamp();
+	if ((ts - last_event) < 5) return;
+	last_event = ts;
+
 	// If we have focus, we get mouse move events on Mac even when the mouse is
 	// outside our client rectangle, we don't want those.
 	if (event.Moving() && !GetClientRect().Contains(event.GetPosition()))

src/audio_display.h

@@ -130,6 +130,9 @@ class AudioDisplay: public wxWindow {
 	/// Zoom level given as a number, see SetZoomLevel for details
 	int zoom_level;
 
+	/// Time since last mouse event
+	long last_event = 0;
+
 	/// Absolute pixel position of the tracking cursor (mouse or playback)
 	int track_cursor_pos = -1;
 	/// Label to show by track cursor