gh-36285: add Rémy Oudompheng's implementation of the BMSS algorithm
The BMSS algorithm computes (the kernel polynomial of) a *normalized*
isogeny from its degree $\ell$ and its domain and codomain in time
$\widetilde O(\ell)$. Currently Sage uses Stark's algorithm for the same
task, which takes time in $\Omega(\ell^2)$. An implementation in Sage of
the BMSS algorithm is available thanks to @remyoudompheng, and in this
patch we add it to the Sage library (following Rémy's suggestion).
Benchmark results for isogenies over a ~280-bit prime field (red is
Stark, blue is BMSS; axes are degree $\ell$ and seconds taken):
URL: https://github.com/sagemath/sage/pull/36285
Reported by: Lorenz Panny
Reviewer(s): github-actions[bot], Kwankyu Lee, Lorenz Panny
