Report audio drops conveniently

[ohmtech-rdi]

One major difference between the simulator and running on the real hardware is the processor used for calculation.
Unless we would have some sort of emulator that could take into account timing of operations, we can't reliably know when a process exceed the time it has to process.

Since Eurorack-blocks' users are not expected to have a STLink debugger (which can be hard to debug when using an integration such as Max or Faust), we need a convenient way to give some feedback to the user when this happens.

One way could be to use the user LED on the DPSM.

We would first need to make sure this is the only (major?) difference we have with the simulator.