Restructure datablocks, unify factory system, and standardize switchable-category API

[AndrewSazonov]

This PR reworks the core EasyDiffraction architecture to use datablocks as the primary model structure and standardize factory-driven categories across experiments, structures, and analysis. This updates the public API around switchable category types, moves calculator selection to the experiment level, removes legacy module layout, and refreshes the architecture docs, tutorials, and test suite to match the new design.

[codecov]

Codecov Report

❌ Patch coverage is 84.36782% with 340 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.84%. Comparing base (6a52ea9) to head (e7cfe2b).

Files with missing lines	Patch %	Lines
...easydiffraction/datablocks/experiment/item/base.py	56.63%	127 Missing and 7 partials ⚠️
.../easydiffraction/datablocks/structure/item/base.py	60.90%	43 Missing ⚠️
src/easydiffraction/analysis/analysis.py	72.72%	31 Missing and 8 partials ⚠️
...diffraction/datablocks/experiment/item/bragg_pd.py	76.08%	20 Missing and 2 partials ⚠️
src/easydiffraction/project/project.py	50.00%	8 Missing and 1 partial ⚠️
src/easydiffraction/core/factory.py	88.23%	5 Missing and 3 partials ⚠️
...rc/easydiffraction/analysis/calculators/crysfml.py	60.00%	6 Missing ⚠️
...atablocks/experiment/categories/peak/cwl_mixins.py	93.33%	6 Missing ⚠️
...atablocks/experiment/categories/peak/tof_mixins.py	92.50%	6 Missing ⚠️
...asydiffraction/datablocks/experiment/collection.py	80.00%	6 Missing ⚠️
... and 18 more

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #128      +/-   ##
===========================================
- Coverage    84.28%   83.84%   -0.44%     
===========================================
  Files           91      124      +33     
  Lines         5911     6544     +633     
  Branches       496      527      +31     
===========================================
+ Hits          4982     5487     +505     
- Misses         746      869     +123     
- Partials       183      188       +5     

Flag	Coverage Δ
integration	70.23% <74.62%> (+0.10%)	⬆️
unittests	72.96% <74.52%> (+1.18%)	⬆️

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