mathlib

453f2183 - refactor(linear_algebra/charpoly): move linear_algebra/charpoly to linear_algebra/matrix/charpoly (#9368)

refactor(linear_algebra/charpoly): move linear_algebra/charpoly to linear_algebra/matrix/charpoly (#9368) We move `linear_algebra/charpoly`to `linear_algebra/matrix/charpoly`, since the results there are for matrices. We also rename some lemmas in `linear_algebra/matrix/charpoly/coeff` to have the namespace `matrix`.