added fit configuration owner #427

[rozyczko]

This pull request refactors how fit configuration is managed in the project, centralizing all minimizer and fitting settings into a new FitSettings class.

Fit Configuration Refactor and Centralization:

• Introduced FitSettings class in fit_settings.py to encapsulate all minimizer selection and configuration, including validation, serialization, and method-specific options.
• Updated Project to store and use a single FitSettings instance (self._fit_settings) instead of separate minimizer fields. All access to minimizer and fit options now go through this object.
• Added new property and setter for fit_settings in Project, ensuring any changes are validated and applied to the next fit.
• Refactored minimizer property and setter in Project to delegate to fit_settings, simplifying the interface and ensuring consistency.

Project Serialization/Deserialization:

• Changed project serialization to store the full fit configuration under fit_settings (with legacy support for fitter_minimizer), and updated loading to use FitSettings.from_dict, collecting any warnings for the user.
• Removed the old DEFAULT_MINIMIZER definition from project.py and re-exported it from fit_settings.py for compatibility.

Public API and Fit Preparation:

• Added a prepare_fit method to Project that prepares a fit using a snapshot of the current fit_settings, supporting advanced workflows and ensuring reproducibility.

[codecov]

Codecov Report

❌ Patch coverage is 97.98489% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.13%. Comparing base (64b4f45) to head (f43a234).

Files with missing lines	Patch %	Lines
src/easyreflectometry/project.py	89.74%	4 Missing ⚠️
src/easyreflectometry/fit_settings.py	98.85%	2 Missing ⚠️
src/easyreflectometry/fitting.py	98.91%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #429      +/-   ##
===========================================
+ Coverage    95.05%   95.13%   +0.08%     
===========================================
  Files           55       56       +1     
  Lines         6006     6249     +243     
===========================================
+ Hits          5709     5945     +236     
- Misses         297      304       +7     

Flag	Coverage Δ
integration	38.29% <45.34%> (+0.89%)	⬆️
unittests	95.13% <97.98%> (+0.08%)	⬆️

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

Files with missing lines	Coverage Δ
src/easyreflectometry/fit_settings.py	98.85% <98.85%> (ø)
src/easyreflectometry/fitting.py	99.09% <98.91%> (-0.40%)	⬇️
src/easyreflectometry/project.py	94.65% <89.74%> (-0.19%)	⬇️

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