Verify comments in fluo deadtime calculations

The algorithm is a little confusing and the comments do not help, we should improve them. Some questions that come to mind:
* `Deadtime is the time after each event during which the detector cannot record another event.` - This seems like a fixed property of the detector, how can we optimise based on it? Or is it the amount of time which we haven't had any events?
* It's still not clear what `reset_ticks` means, we should rename to something more sensible