Resolve "Revamp EPA to include position-dependence"

Description

Re-structuring the EPA module to:

• add transparency
• allow for ion initial states in a more coherent way
• add new form factors (e.g. Wood-Saxon etc. for ions)
• improve the handling in the impact parameter plane, relevant for rescattering

Test Plan

We can compare/plot form factors with the EPA_Spectra_Plotter. This includes:

• checks of numerical integration (for example for q^2 integrals of point-like, Gauss and dipole form factors with analytic expressions)
• check the numerical integration for N(x,b) with analytic results for point-like particles
• check MC vs. analytics for b*N(x,b), relevant for the positioning in impact parameter space (transverse plane)
• check cross sections

Example Result

• some first plots in the overleaf

Additional Checklist Items

• I have updated documentation as needed
• I considered if this should be cherry-picked/ported somewhere else (rel-2-x or master), and if yes, opened a corresponding issue or MR

I will update documentation etc. together with the "big" amisic MR

Closes #576