Add a class PowerSeries_pari for power series based on PARI's t_SER type. At least if the base ring is a finite field, this is much faster than the existing implementation based on NTL polynomials.

Depends on #20062
Depends on #21755
Depends on #22210
Depends on #22212

Component: algebra

Keywords: pari series performance

Author: Peter Bruin

Branch/Commit: 2c9cb8a

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/15601