feat(data/mv_polynomial/basic): add is_scalar_tower and smul_comm_class instances (#6542)
feat(data/mv_polynomial/basic): add is_scalar_tower and smul_comm_class instances (#6542)

This also fixes the `semimodule` instance to not require `comm_semiring R`







leanprover-community/mathlib,leanprover-community/mathlib