bpo-43420: Simple optimizations for Fraction's arithmetics (GH-24779)

bpo-43420: Simple optimizations for Fraction's arithmetics (GH-24779)

bpo-43420: Implement standard transformations in + - * / that can often reduce the size of intermediate integers needed. For rationals with large components, this can yield dramatic speed improvements, but for small rationals can run 10-20% slower, due to increased fixed overheads in the longer-winded code. If those slowdowns turn out to be a problem, see the PR discussion for low-level implementation tricks that could cut other fixed overheads.

Co-authored-by: Tim Peters <tim.peters@gmail.com>
Co-authored-by: Mark Dickinson <dickinsm@gmail.com>