scipy.interpolate.interp1d may be removed in future scipy version

[JanWeldert]

We use from scipy.interpolate import interp1d in multiple parts of the code, namely

• pisa/pisa/core/prior.py

  Line 14 in cfeb9b4

  from scipy.interpolate import splev, splrep, interp1d

• pisa/pisa/stages/background/atm_muons.py

  Line 7 in cfeb9b4

  from scipy.interpolate import interp1d

• pisa/pisa/utils/spline_smooth.py

  Line 10 in cfeb9b4

  from scipy.interpolate import splrep, splev, interp1d

• The new stage introduced in #Revive parametric Aeff stage #798

At the moment we are safe because we limit the scipy version, but in the future when we allow for newer versions of scipy this might become a problem.

[thehrh]

I'm finding a few more occurrences: https://github.com/search?q=repo%3Aicecube%2Fpisa%20interp1d&type=code

[thehrh]

Scipy docs suggest the following replacement for "broken-line" interpolation: https://docs.scipy.org/doc/scipy/tutorial/interpolate/1D.html#piecewise-linear-interpolation

[JanWeldert]

But in the numpy version you have to do the interpolation again every time you want to evaluate it.