Speed up evaluation of FDataGrid

[vnmabus]

• Vectorizes interpolation of FDataGrid using the "new" SciPy API.
• Removes spline smoothing functionality from interpolators, as it was not true interpolation and was not vectorizable.
• Due to some Scipy limitations not all interpolation orders are available in oldest SciPy versions for every domain dimension. As interpolation is rarely changed, though, and most algorithms do not interpolate, we will break backwards compatibility here to achieve vectorization.
• In the rare cases where a user needs the old behaviour, they can always create their own interpolation class from the old code.

[codecov[bot]]

Codecov Report

Merging #474 (e607b3f) into develop (88e5225) will decrease coverage by 0.02%. The diff coverage is 86.04%.

@@             Coverage Diff             @@
##           develop     #474      +/-   ##
===========================================
- Coverage    84.80%   84.77%   -0.03%     
===========================================
  Files          130      130              
  Lines        10522    10465      -57     
===========================================
- Hits          8923     8872      -51     
+ Misses        1599     1593       -6     

Impacted Files	Coverage Δ
...kfda/exploratory/stats/_functional_transformers.py	92.85% <ø> (ø)
...ing/feature_construction/_function_transformers.py	100.00% <ø> (ø)
skfda/representation/interpolation.py	84.12% <85.36%> (-2.54%)	:arrow_down:
skfda/tests/test_interpolation.py	99.20% <100.00%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.