tud_task() should provide a way to indicate if it did anything

[ReimuNotMoe]

I'm attempting to make my firmware fully tickless, which means, the CPU will go to sleep when nothing can be done and only the peripheral interrupts can wake it up.

In this way, each task in the main loop must indicate if they did anything in the current loop invocation. Now I have to modify tud_task() to make it indicate it's busy when it received something from the queue.

So IMO it's better to provide a standardized API to let the TinyUSB stack report its busy status. Such a mechanism is also mandatory when using TinyUSB on Linux (using /dev/mem or UIO) because a non-stop while (1) loop will eat up all the CPU.