signal predictions from axial currents

[espenhgn]

Is your feature request related to a problem? Please describe.
We could use a separate class implementation of magnetic field predictions from compartmental axial currents (via the Biot-Savart law). Main motivation would be ease of use, e.g., with output from LFPy (https://lfpy.readthedocs.io/en/v2.2.6/classes.html?highlight=get_axial_currents_from_vmem#LFPy.Cell.get_axial_currents_from_vmem) or recorded axial currents from Arbor (https://docs.arbor-sim.org/en/latest/python/probe_sample.html?highlight=axial#arbor.cable_probe_axial_current)

Describe the solution you'd like
A new class, perhaps wrapping the existing class eegmegcalc.InfiniteHomogeneousVolCondMEG (https://lfpykit.readthedocs.io/en/latest/#class-eegmegcalc-infinitehomogeneousvolcondmeg) set up for equivalent current dipoles.

Such class(es) could be put in a new submodule lfpykit.iaxial.* or similar.

Edit: Forgot that we already in LFPy have patched in a function InfiniteHomogeneousVolCondMEG.calculate_H_from_iaxial(cell) (https://lfpy.readthedocs.io/en/latest/classes.html?highlight=InfiniteHomogeneousVolCondMEG#LFPy.InfiniteHomogeneousVolCondMEG.calculate_H_from_iaxial)