[Feature Request] timer interrupt callback function

It would be nice if there was a possibility to implement a way to add some own code in the timer interrupt routine. That could be accomplished like it is done in "WInterrupts".

Possible applications:
sampling rotary encoders
sampling tachometer signals
acceleration/deceleration
fading

Start by examining the existing WInterrupts approach and the timer interrupt API in ArduinoCore-API. Determine how a user callback could be exposed for the listed applications while preserving the hardware-independent API, then define tests or examples that show the callback can be registered and invoked safely.

Written by the indexing model from the issue text.