Build basic consistency checking into the models

julia> p = RodCellParams(maxlength=0.0, radius = 1.0)   # this really really should error
RodCellParams(l ≈  0.00, Y ≈  1.0000e+04, r ≈  1.00)

julia> InPartSBiome.restlength(0.0, p)
-1.0

Sadly, it is even possible to run entire cluster simulations with such malformed model parameters.