Correct weighted R-factor calculations and document reliability metrics

[AndrewSazonov]

Use inverse-variance weights for wR calculations and document all reported reliability-factor equations. Add regression coverage for importing the ICSD ZrW₂O₈ CIF, including ionic atom symbols and cryspy conversion, and simplify the LaM₇O₃ tutorial sidebar label.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.39%. Comparing base (c4ae7e8) to head (5755d2d).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #224      +/-   ##
===========================================
- Coverage    90.40%   90.39%   -0.01%     
===========================================
  Files          284      284              
  Lines        24792    24789       -3     
  Branches      2910     2909       -1     
===========================================
- Hits         22412    22409       -3     
  Misses        1754     1754              
  Partials       626      626              

Flag	Coverage Δ
unittests	90.39% <100.00%> (-0.01%)	⬇️

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Files with missing lines	Coverage Δ
src/easydiffraction/analysis/analysis.py	93.63% <100.00%> (-0.02%)	⬇️
...rc/easydiffraction/analysis/fit_helpers/metrics.py	92.98% <100.00%> (+0.12%)	⬆️

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