Feature: Add fll_program_signal_check_loop() and fll_program_signal_check_simple().

Feature: Add fll_program_signal_check_loop() and fll_program_signal_check_simple().

These functions are already implemented in each of the level 3 programs.
The functions are pretty much identical.
Move the signal check logic into the `fll_program` project as `fll_program_signal_check_loop()` and `fll_program_signal_check_simple()`.

Update all of the programs, removing their variation and instead using one of these two.
Utilize a macro to call one or the other based on thread enabled state.

The fss_write payload is not calling the fss_write function and is instead using its own variation.
Replace that code with the macro as well.

Remove all stale and no longer needed signal check defines.