Is Tobyfit still supporting only one unique instrument?

[abuts]

get_inst_class function of sqw class used in @sqw/tobyfit and @sqw/resolution_plot and tested in test_sqw_class-->test_migrated_api throws if non-unique instrument is attached to the class.

This is easy changeable, but then what would usage scenario in the places above would be?
The issue should be clarified and fixed.

After discussion with Toby we see that this is not the case and substantial changes in the logic of the methods have to be done.
Single instrument is not sufficient any more.

Need thinking and decision on what is the right thing to be doing if more then one instrument is there.

The equivalent description was found in #902. Those is the duplicate of this one so is closed:
get_inst_class function has been modified after unique object container become the part of experiment. Old implementation was failing when multiple different instruments were identified in the container. I have currently modified it to support this behavior but apparently Tobyfit should support multiple instruments.

How get_inst_class function should be modified to support multiple instruments and do these modifications to the function