tobyfit_resconv_DG_disk/tobyfit_resconv_DG_fermi do not have unit tests for all possible space of input parameters

[abuts]

Work with Re #1755 have identified that crystal alignment part, related to sqw method refine_crystal_strip_pars have been broken.

While refine_crystal_strip_pars have been formaly fixed under Re #1755, its unclear if the fixture is correct as purpose of the original code is unclear.

The issue is caused by tobyfit_resconv_DG_disk/tobyfit_resconv_DG_fermi method not having unit tests for all possible set of input parameters, including change, caused by refine_crystal_strip_pars usage.

From Re #1755 point of view, I can not even identify what these tests shcould verify. In addition to that, tobyfit_resconv_DG_disk and tobyfit_resconv_DG_fermi have 90% of code in common

These method may contain other errors and common code highly increase the code maintenance cost so the issue should be fixed