Add optional argument use_pylops to pyfaust.lazylinop.kron and zpad and...

Add optional argument use_pylops to pyfaust.lazylinop.kron and zpad and enablediag_opt optimization in pyfaust.dft call of lazylinop.convolve2d.

It allows to get the same performance as in Simon's notebook (https://gitlab.inria.fr/delamare/faust_xp/-/blob/main/nb/2d.ipynb).
pylops is now a pip dependency of pyfaust.