[FEATURE]: Adaptive-area “pr cm2” monitor

[willend]

Is your feature request related to a problem? Please describe.

• The Monitor_nD(options=“per cm2… “ feature for measuring flux is nice, yet normalises to whatever fixed geometry is provided on initialisation. (In other words, to ensure a correct flux measurement the monitor should be fully illuminated.

Describe the solution you'd like

• I would like the addition of a simple, flat monitor that makes a statistical analysis of the beam, estimates the beam footprint area (discarding outliers) and uses that as normalisation term. (i.e. event-oriented monitor that ends up histogramming during SAVE

Describe alternatives you've considered

• It may be that this is readily available within Monitor_nD somehow, in that case a richer documentation would be a solution?

Additional context

• Demo-instr attached here, includes %Example strings for illustration
  percm2.instr.txt

[willend]

@ikibalin FYI