- avoid the possibility of unsigned underflow from subtracting two HRT timestamps (uint64_t)
- most of these aren't problematic, but people tend to replicate the pattern, so it's better to be safe
- likely wasn't a problem when people were using hrt_absolute_time() in place, but if using an existing timestamp there's the possibility it's older than a more recent topic update
- print list of events whenever they change if
CONSOLE_PRINT_ARMING_CHECK_EVENT is set, instead of on each update call
- reduce flash usage by moving out templated code into non-template method