Interim updates

[rozyczko]

This pull request adds support for progress callbacks during fitting operations. The main goal is to allow users to receive progress updates and optionally cancel fits in progress. Added progress_callback parameter and a way to handle cancellation gracefully.

• Added an optional progress_callback parameter to the fit methods in Fitter, MinimizerBase, MultiFitter and all minimizer subclasses, allowing users to receive iterative progress updates and cancel fits.

• Implemented progress callback integration in LMFit: added _create_iter_callback to wrap the user callback, constructed detailed progress payloads, and enabled fit cancellation by raising a new FitCancelled exception. Ensured parameter values are restored on cancellation or error.

• Added the FitCancelled exception class to signal user-requested cancellation, and ensured proper restoration of parameter values on cancellation or error.

[github-actions]

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[rozyczko]

Required for easyscience/EasyReflectometryApp#290