bigint: simplify Hash
bigint: simplify Hash

There cannot be any leading zeros in a BigUint so just derive Hash which will just hash the Vec directly.
Add Hash to Sign so we can derive it for BigInt as well.

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