Allows FDCT to be picklable so they can be used with BlockDiag(nproc>1)

[cako]

Description

Allows FDCT to be picklable so they can be used with BlockDiag(nproc>1)

Changes

• Implements __getstate__ and __setstate__ in base FDCT.

Test script

import numpy as np

from pylops import BlockDiag
from curvelops import FDCT2D

nr = 10
ns = 312
nt = 1016

nbscales = 4
nbangles_coarse = 8
allcurvelets = False

DCTOp = FDCT2D((ns, nt), nbscales=nbscales,
    nbangles_coarse=nbangles_coarse,
    allcurvelets=allcurvelets, dtype="complex64")

DCTOp1 = DCTOp.H

SopDiag = []
for i in range(nr):
    SopDiag.append(DCTOp1)
SopDiag = BlockDiag(SopDiag, nproc=2)

data = np.zeros(SopDiag.shape[1])
SopDiag @ data # This errors in the main branch