Support underscore-style CIF structure tags

[AndrewSazonov]

Accept both dotted and underscore-style CIF tags when importing structures. This also adds support for charged atom type symbols and ensures CrysFML receives bare element symbols. Includes regression tests for legacy cell and atom-site tags.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.38%. Comparing base (883c384) to head (9ccde9f).
⚠️ Report is 133 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #222      +/-   ##
===========================================
+ Coverage    82.26%   90.38%   +8.12%     
===========================================
  Files           88      284     +196     
  Lines         5451    24789   +19338     
  Branches       454     2910    +2456     
===========================================
+ Hits          4484    22405   +17921     
- Misses         802     1755     +953     
- Partials       165      629     +464     

Flag	Coverage Δ
integration	?
unittests	90.38% <100.00%> (+17.93%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...rc/easydiffraction/analysis/calculators/crysfml.py	69.74% <100.00%> (+21.59%)	⬆️
...ablocks/structure/categories/atom_sites/default.py	88.33% <100.00%> (ø)
src/easydiffraction/io/cif/handler.py	82.60% <100.00%> (-17.40%)	⬇️
src/easydiffraction/utils/utils.py	98.08% <100.00%> (+34.66%)	⬆️

... and 325 files with indirect coverage changes

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