Simplify BigInt Mul forwarding
Simplify BigInt Mul forwarding

rust-num/num-bigint,vks/num,DonSheddow/num,rust-num/num-integer,anchovieshat/num,rust-num/num,rust-lang/num,rust-lang/num,rust-num/num-traits,rust-num/num,DonSheddow/num,rust-num/num-bigint,jbcrail/num,anchovieshat/num,vks/num,koverstreet/num,koverstreet/num,jbcrail/num,rust-num/num-integer,rust-num/num-traits