Refactor fit modes and sequential analysis workflow

[AndrewSazonov]

• Reworks the fitting API around analysis.fitting, analysis.fitting_mode_type, and the mode-specific joint_fit, sequential_fit, and sequential_fit_extract categories.
• Makes analysis.fit() the execution entry point for single, joint, and sequential fitting, with CIF serialization/load support for the new model.
• Adds persisted sequential-fit settings, CSV result replay/resume support, and diffrn.* extraction handling.
• Updates CLI behavior, tutorials, docs, package-structure docs, and test coverage for the new fitting surfaces.
• Includes follow-up improvements to sequential progress rendering, fit-series plotting, ASCII output, and related analysis/reporting helpers.

[codecov]

Codecov Report

❌ Patch coverage is 79.62771% with 197 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.01%. Comparing base (1a94b59) to head (2a618b0).
⚠️ Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/easydiffraction/io/cif/serialize.py	55.33%	33 Missing and 13 partials ⚠️
src/easydiffraction/display/plotting.py	40.00%	38 Missing and 7 partials ⚠️
src/easydiffraction/analysis/analysis.py	77.77%	24 Missing and 12 partials ⚠️
src/easydiffraction/analysis/sequential.py	86.60%	15 Missing and 15 partials ⚠️
src/easydiffraction/display/plotters/ascii.py	72.22%	5 Missing and 5 partials ⚠️
src/easydiffraction/project/project.py	71.42%	6 Missing and 4 partials ⚠️
src/easydiffraction/core/guard.py	63.63%	7 Missing and 1 partial ⚠️
src/easydiffraction/display/progress.py	73.68%	3 Missing and 2 partials ⚠️
...lysis/categories/sequential_fit_extract/default.py	95.94%	3 Missing ⚠️
src/easydiffraction/core/variable.py	81.81%	1 Missing and 1 partial ⚠️
... and 2 more

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #175      +/-   ##
===========================================
- Coverage    86.43%   86.01%   -0.42%     
===========================================
  Files          159      168       +9     
  Lines        12549    13231     +682     
  Branches      1463     1557      +94     
===========================================
+ Hits         10847    11381     +534     
- Misses        1177     1275      +98     
- Partials       525      575      +50     

Flag	Coverage Δ
integration	70.00% <68.04%> (-0.34%)	⬇️
unittests	78.34% <70.52%> (+<0.01%)	⬆️

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

Files with missing lines	Coverage Δ
src/easydiffraction/__main__.py	83.78% <100.00%> (+0.45%)	⬆️
src/easydiffraction/analysis/__init__.py	100.00% <100.00%> (ø)
...rc/easydiffraction/analysis/categories/__init__.py	100.00% <100.00%> (ø)
...iffraction/analysis/categories/fitting/__init__.py	100.00% <100.00%> (ø)
...diffraction/analysis/categories/fitting/default.py	100.00% <100.00%> (ø)
...diffraction/analysis/categories/fitting/factory.py	100.00% <100.00%> (ø)
...fraction/analysis/categories/joint_fit/__init__.py	100.00% <100.00%> (ø)
...ffraction/analysis/categories/joint_fit/default.py	100.00% <100.00%> (ø)
...ffraction/analysis/categories/joint_fit/factory.py	100.00% <100.00%> (ø)
...ion/analysis/categories/sequential_fit/__init__.py	100.00% <100.00%> (ø)
... and 23 more

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