Handle shared experiment models when converting to cambridge frame in mtz export

[jbeilstenedmands]

If an experiment list has shared experiment models e.g. shared Beam model, the transformations end up being attempted multiple times as the function loops over experiments. I found that this caused a crash in the rotate beam function, but in theory it could lead to an issue in any shared model. So simply make a deepcopy of the model if the model is shared.

[dagewa]

Good spot. As MTZ does not handle shared models anyway, making distinct copies first to simplify later bookkeeping makes sense.

[codecov]

Codecov Report

Merging #2182 (07b943c) into main (3543e58) will decrease coverage by 0.09%.
The diff coverage is 14.28%.

@@            Coverage Diff             @@
##             main    #2182      +/-   ##
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- Coverage   80.66%   80.57%   -0.10%     
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  Files         588      588              
  Lines       66581    66595      +14     
  Branches     9384     9392       +8     
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- Hits        53707    53658      -49     
- Misses      10798    10853      +55     
- Partials     2076     2084       +8     

[jbeilstenedmands]

I think this might also need backporting to the LTS branch, as it fixes a bug introduced in #2054 which was also backported to the LTS branch