[cadenmyers13]

Deprecating diffpy.srfit.structure in favor of diffpy.cmistructure.

This PR emits the deprecation warning on import:

>>> import diffpy.srfit.structure
DeprecationWarning: 'diffpy.srfit.structure'
is deprecated and will be removed in version 4.0.0. Please use 'diffpy.cmistructure' instead.

and if a function is called:

DeprecationWarning: 'diffpy.srfit.structure.sgconstraints.constrainAsSpaceGroup' is 
deprecated and will be removed in version 4.0.0. Please use 
'diffpy.cmistructure.sgconstraints.constrain_as_space_group' instead.

The attribute stru is also deprecated:

DeprecationWarning: 'diffpy.srfit.structure.basestructureparset.BaseStructureParSet.stru' is 
deprecated and will be removed in version 4.0.0. Please use 
'diffpy.cmistructure.basestructureparset.BaseStructureParSet.structure' instead.
  super(RecipeContainer, self).__setattr__(name, value)

[cadenmyers13]

This fixture is left here because it is only used in the deprecation tests so we want to remove it when all the tests are removed. If we don't, this will hang around in conftest.py unused

[cadenmyers13]

@sbillinge ready for review. deprecation of diffpy.srfit.structure

[codecov]

Codecov Report

❌ Patch coverage is 85.00000% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.97%. Comparing base (507aa4e) to head (b571573).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
tests/deprecated/test_structure_deprecations.py	85.00%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #236      +/-   ##
==========================================
+ Coverage   84.95%   84.97%   +0.01%     
==========================================
  Files          44       45       +1     
  Lines        4886     4945      +59     
==========================================
+ Hits         4151     4202      +51     
- Misses        735      743       +8     

Files with missing lines	Coverage Δ
tests/test_sgconstraints.py	11.65% <ø> (+0.07%)	⬆️
tests/deprecated/test_structure_deprecations.py	85.00% <85.00%> (ø)

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