Implement `BaSiC.fit()`

[Nicholas-Schaub]

This task will create a baseline implementation of the BaSiC algorithm. It should copy the implementation from the main branch and adapt it to work with the Settings or BaSiC settings and store the flatfield/darkfield images as class attributes.

• Implement the BaSiC algorithm from the main branch
• Change the current images input parameter from Iterable[np.ndarray] to np.ndarray.
• Add unit tests for BaSiC.fit()