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

❌ Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (a472411) to head (0f9e6e5).

Files with missing lines	Patch %	Lines
src/easyreflectometry/fitting.py	0.00%	4 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           develop    #383   +/-   ##
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  Coverage     0.00%   0.00%           
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  Files           42      42           
  Lines         3578    3581    +3     
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- Misses        3578    3581    +3     

Flag	Coverage Δ
integration	0.00% <0.00%> (ø)
unittests	0.00% <0.00%> (ø)

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Files with missing lines	Coverage Δ
src/easyreflectometry/analysis/bayesian.py	0.00% <ø> (ø)
src/easyreflectometry/fitting.py	0.00% <0.00%> (ø)

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