Add SPODI refinement tutorial and improve fitting controls

[AndrewSazonov]

• Adds a staged YAlO₃/Al₂O₃ refinement tutorial using SPODI data, with automatic background estimation, model-based background refinement, and a generated notebook.
• Introduces readable, method-specific convergence tolerances with dynamic settings, backend mappings, documentation, and tests. Applicable tutorials use chi_square_change_tolerance = 1e-2 to reduce documentation build time.
• Warns about unsupported ionic atom symbols, applies documented scattering-factor fallbacks, and keeps notebook warnings on one line.
• Records free-parameter counts in tutorial baselines.

[codecov]

Codecov Report

❌ Patch coverage is 93.77778% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.42%. Comparing base (5e3ea2a) to head (297f6e1).

Files with missing lines	Patch %	Lines
...ablocks/structure/categories/atom_sites/default.py	81.25%	4 Missing and 2 partials ⚠️
src/easydiffraction/analysis/minimizers/bumps.py	66.66%	1 Missing and 3 partials ⚠️
src/easydiffraction/analysis/calculators/cryspy.py	94.59%	1 Missing and 1 partial ⚠️
...fraction/analysis/categories/minimizer/lsq_base.py	97.14%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #227      +/-   ##
===========================================
+ Coverage    90.39%   90.42%   +0.02%     
===========================================
  Files          284      284              
  Lines        24789    24992     +203     
  Branches      2909     2926      +17     
===========================================
+ Hits         22409    22600     +191     
- Misses        1754     1761       +7     
- Partials       626      631       +5     

Flag	Coverage Δ
unittests	90.42% <93.77%> (+0.02%)	⬆️

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	70.85% <100.00%> (+1.10%)	⬆️
...diffraction/analysis/categories/minimizer/bumps.py	100.00% <100.00%> (ø)
...tion/analysis/categories/minimizer/bumps_amoeba.py	100.00% <100.00%> (ø)
...fraction/analysis/categories/minimizer/bumps_de.py	100.00% <100.00%> (ø)
...fraction/analysis/categories/minimizer/bumps_lm.py	100.00% <100.00%> (ø)
...diffraction/analysis/categories/minimizer/dfols.py	100.00% <100.00%> (ø)
...diffraction/analysis/categories/minimizer/lmfit.py	100.00% <100.00%> (ø)
...alysis/categories/minimizer/lmfit_least_squares.py	100.00% <100.00%> (ø)
...ion/analysis/categories/minimizer/lmfit_leastsq.py	100.00% <100.00%> (ø)
...asydiffraction/analysis/minimizers/bumps_amoeba.py	100.00% <100.00%> (ø)
... and 12 more

... and 1 file with indirect coverage changes

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