chore(data/polynomial/monic): speedup next_coeff_mul (#4920)
chore(data/polynomial/monic): speedup next_coeff_mul (#4920)



Co-authored-by: Bryan Gin-ge Chen <6e05157ce10643a7cfc5a3d4e29e4fa5cffe1fc6@gmail.com>

leanprover-community/mathlib,leanprover-community/mathlib