chore(data/matrix/basic): clean up of new lemmas on matrix numerals (#2996)
chore(data/matrix/basic): clean up of new lemmas on matrix numerals (#2996)

Generalise and improve use of `@[simp]` for some newly added lemmas about matrix numerals.



Co-authored-by: Scott Morrison <63f04b4d96235eb042cc46d94f14d241d2a26722@gmail.com>

leanprover-community/mathlib,leanprover-community/mathlib