gui lens alignement: tentative to fix move to center

on actual tests, it seems it went the opposite way, so inverting the angle should fix it

still need tests.
semcomedi: remove unused functions

already too big, let's not keep unused code
semcomedi: improve settling by making it proportional to the ROI size

Espcially, spot mode should now be the actual duration of a dwell time, and not 2x longer.
semcomedi: add duplication rate to find_best_oversampling_rate

also some more tweaking to find_best_oversampling_rate(), to avoid cases where only the lowest read period would be tried

remove find_closest_dwell_time() not needed anymore
semcomedi: use dpr

allows to have very long dwell times

Useful for the SPARC, where 4s per point is not considered long.

Still needs to be tested on real hardware