[Enhancement] Add 1D Theis solution

[MuellerSeb]

This solution is missing (34a):

[MuellerSeb]

Barker, J.A., 1988. A generalized radial flow model for hydraulic tests in fractured rock, Water Resources Research, vol. 24, no. 10, pp. 1796-1804.

[MuellerSeb]

For now, one can use the grf model:

grf(time=time, rad=rad, storage=1e-4, conductivity=1e-4, rate=-1e-4, dim=1)