@spec cancel([reference()]) :: list()

Cancels a list of timer references to stop scheduled timer messages.

• timer_refs is a list of references returned by Process.send_after/3.
• If a nil timer_ref is encountered, logs a debug message and skips cancellation.

@spec send_timer({0 | 1, integer(), integer()}) :: nil | reference()

Schedules the next timer message for LED blinking or repeating patterns.

• Accepts a tuple {state, interval, times} where:

  • state is 0 (off) or 1 (on).
  • interval is the delay in milliseconds before sending the next message.
  • times is the number of remaining toggles; -1 means infinite repeats.

• If times is -1, schedules the timer infinitely.

• If times is 0, does nothing (no timer scheduled).

• If state is 0, decrements times and schedules the next timer.

• If state is 1, schedules the next timer without decrementing times.

Returns the timer reference or nil if no timer is scheduled.