Operetta/Phenix: calculate physical Z size in micrometers

[melissalinkert]

Fixes #4240 (cc @mabruce).

showinf -nopix -omexml on curated/perkinelmer-operetta/public/omer/ without this change should show a PhysicalSizeZ that is very small, and in dm units. With this change, the PhysicalSizeZ should be in µm units, and large enough to not round to 0.

This does require a configuration update, which does flag that two sample plates now have a PhysicalSizeZ of 1µm. See forthcoming configuration PR.

Adding to 8.0.1 for initial evaluation, but this can easily be moved to a later milestone.

[sbesson]

While this file format internally supports different length units and nanometers are typically used for excitation wavelength, several quantities including ImageResolutionX, ImageResolutionY, PositionX, PositionY, PositionZ are notoriously stored as meters using scientific notations for their values. This statement applies for all the representative samples in the curated OME QA repository.

The reader internally converts the values of ImageResolutionX and ImageResolutionY into micrometers when populating the Pixels.PhysicalSize{X,Y} values since the introduction of the reader in #22. Note this logic might also reflect the vestige of a time where the OME data model did not support alternative units and the physical sizes had to be stored as micrometers. However, looking at all representative samples, this matches the actual scale of every data acquired by this instrument and received so far and provides a much better user experience for any tool aiming to display this metadata.

In that sense, the change proposed in this PR simply updates the handling of the physical size alongside Z to match the exact same assumptions as the other physical sizes and improves both the reader consistency as well as the user experience.