Improve test comments under @pytest.mark.parametrize in test_diffraction_objects.py

[bobleesj]

Some battle-tested practices being adopted:

• Replace UC to C
• Add higher-level test function comment before starting "C"
• Use "x, y, z (provided), expect blah blah blah" format for consistency

cc' @yucongalicechen

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.68%. Comparing base (8107874) to head (499a1c3).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #273   +/-   ##
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  Coverage   98.68%   98.68%           
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  Files           8        8           
  Lines         379      379           
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  Hits          374      374           
  Misses          5        5           

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

[bobleesj]

@sbillinge ready for review.

@yucongalicechen , the part that is remaining is the test_scale_to function.

The existing comments like# C2: Same length x-arrays with exact x-value match, # C3: Same length x-arrays with approximate x-value match were abit hard for me to understand what's being tested. Would you mind improving this test comments for test_scale_to using the above format?

[bobleesj]

(Just added a quick fix) pls see my comments right above