[DSSC][Dark][Correct] Remove options check for num_cells and move it into dssclib and add deviation

Description

This MR address: https://git.xfel.eu/calibration/planning/-/issues/199 and the next step for !918 (merged)

• Move get_num_cells from dark and correction notebook into dssclib
• Update get_num_cells to return max number of cells.
• Add a deviation for memory cells in the dark constants to be able to retrieve darks from 0 to N

How Has This Been Tested?

• TBD

Relevant Documents (optional)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Checklist:

Reviewers

@schmidtp @danilevc