[cadenmyers13]

What problem does this PR address?

set_structure now takes whichever form of structure the user has, either a Path, ParameterSet, or structure object. This essentially merges set_structure_from_parset into set_structure which simplifies the code a bit. I found this slightly confusing when i first started writing cmi code.

A structure object (unchanged):

generator.set_structure(structure)          # parameters under generator.phase

A ParameterSet, used as it is, with its own name. Giving one ParameterSet to several generators shares the structure:

phase = structure_to_parameter_set("ni", structure)
xray_generator.set_structure(phase)
neutron_generator.set_structure(phase)      # both under .ni, shared

The path to a structure file, as a Path or str, read with diffpy.structure.load_structure:

generator.set_structure(Path("ni.cif"))     # parameters under generator.phase

name with a ParameterSet raises an error. A ParameterSet keeps its own name. Renaming it would rename it in every generator that shares it, so name can only be used with a structure or a path:

phase = structure_to_parameter_set("phase", structure)
generator.set_structure(phase, name="ni")
# ValueError: set_structure was given the name 'ni' with a ParameterSet, which
# keeps its own name, 'phase'. Please leave out the name, or give it when you
# create the ParameterSet.

name now defaults to None, so set_structure can tell whether one was given. For a structure or a path, it still means "phase". set_structure_from_parset is unchanged, so existing scripts keep working.

[cadenmyers13]

@sbillinge ready for review

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.31%. Comparing base (fe9d2c7) to head (f6387a9).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #20      +/-   ##
==========================================
+ Coverage   97.05%   97.31%   +0.26%     
==========================================
  Files           6        6              
  Lines         340      373      +33     
==========================================
+ Hits          330      363      +33     
  Misses         10       10              

Files with missing lines	Coverage Δ
tests/test_generators.py	100.00% <100.00%> (ø)

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[cadenmyers13]

@sbillinge ready for review now