Last minute hot fix for the GD32 Arduino core not autoflushing once per ms.

Tested to work on both a Model 01 and a Model 100. This will become
unnecessary when the GD32 Arduino core grows the ability to autoflush on
SOF packets from the host

plugins/Kaleidoscope-FocusSerial/src/kaleidoscope/plugin/FocusSerial.cpp

@@ -37,6 +37,8 @@ char FocusSerial::command_[32];
 uint8_t FocusSerial::buf_cursor_ = 0;
 
 EventHandlerResult FocusSerial::afterEachCycle() {
+  // GD32 doesn't currently autoflush the very last packet. So manually flush here
+  Runtime.serialPort().flush();
   // If the serial buffer is empty, we don't have any work to do
   if (Runtime.serialPort().available() == 0) {
     return EventHandlerResult::OK;