gh-36971: add helper method to concatenate vectors
Writing `vector(R, list(v) + list(w))` is a common way to concatenate
two vectors `v` and `w` over some ring `R`.
In this patch we introduce a simple helper method which allows writing
`v.concatenate(w)` instead.
URL: https://github.com/sagemath/sage/pull/36971
Reported by: Lorenz Panny
Reviewer(s): grhkm21, Ruchit Jagodara
