High-order FD time derivative for SINDy

[dreamer2368]

• fd module provides high-order, summation-by-parts finite-difference operators.
  • This is proven to approximate time derivative better.
• sindy.compute_sindy_data is replaced with sindy.compute_time_derivative
  • compute_time_derivative returns the time-derivative array with the same shape of the original solution time series.
  • takes additional input for FD type, to specify the FD operator to use.
  • All the routines involving this routine also take the additional input for FD type.

In future, SINDy part should be factored out from BayesianLaSDI class, in order to support various types of SINDy formulation.