Core fixes

[rozyczko]

This pull request refactors the MCMC sampling interface in easyreflectometry to use the new core Sampler class instead of the older MultiFitter.mcmc_sample() method. The migration improves API clarity and aligns with upstream changes in the easyscience dependency. The tests have been updated to mock and verify the new Sampler-based workflow, ensuring parameter forwarding, result handling, and proper integration. Documentation has also been updated to reflect these changes.

Core API migration

• Updated the MCMC sampling implementation in fitting.py to use the core Sampler class for sampling, replacing direct calls to MultiFitter.mcmc_sample(). The new approach constructs a Sampler and calls its sample() method, forwarding all relevant parameters and returning a standardized result dictionary.
• Updated the dependency in pyproject.toml to use the bayesian_extend branch of easyscience, which provides the new Sampler API.

Documentation updates

• Updated docstrings in bayesian.py to reference the new Sampler API and its methods for extending chains, instead of the deprecated MultiFitter.mcmc_sample().

Test suite modernization

• Refactored tests in test_fitting.py to mock and patch the new Sampler class, verifying that parameters are correctly forwarded and results are handled as expected. Removed mocks and references to the old mcmc_sample method, and added helpers to simulate Sampler behavior.
• Added import for patch from unittest.mock to facilitate mocking of the Sampler class in tests.

API surface

• Added direct import of Sampler in fitting.py to support the new sampling workflow.

[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 51.13%. Comparing base (90fed4f) to head (c50fd8b).

Additional details and impacted files

@@             Coverage Diff              @@
##           develop     #383       +/-   ##
============================================
+ Coverage     0.00%   51.13%   +51.13%     
============================================
  Files           42       48        +6     
  Lines         3573     3849      +276     
============================================
+ Hits             0     1968     +1968     
+ Misses        3573     1881     -1692     

Flag	Coverage Δ
integration	31.61% <27.39%> (+31.61%)	⬆️
unittests	50.01% <95.89%> (+50.01%)	⬆️

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

Files with missing lines	Coverage Δ
src/easyreflectometry/analysis/bayesian.py	13.80% <ø> (+13.80%)	⬆️
...c/easyreflectometry/calculators/calculator_base.py	87.80% <100.00%> (+87.80%)	⬆️
src/easyreflectometry/calculators/factory.py	88.23% <100.00%> (+88.23%)	⬆️
...rc/easyreflectometry/calculators/refl1d/wrapper.py	63.72% <ø> (ø)
src/easyreflectometry/calculators/refnx/wrapper.py	85.48% <100.00%> (ø)
src/easyreflectometry/fitting.py	52.38% <100.00%> (+52.38%)	⬆️
src/easyreflectometry/limits.py	96.15% <100.00%> (+96.15%)	⬆️
src/easyreflectometry/model/model.py	68.46% <100.00%> (+68.46%)	⬆️
...rc/easyreflectometry/model/resolution_functions.py	82.35% <100.00%> (+82.35%)	⬆️
src/easyreflectometry/project.py	49.45% <100.00%> (+49.45%)	⬆️
... and 4 more

... and 32 files with indirect coverage changes

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