bnToHex function
Implementation
String bnToHex(BigInt bn,
{int bitLength = -1, Endian endian = Endian.big, bool isNegative = false}) {
var u8a =
bnToU8a(bn, bitLength: bitLength, endian: endian, isNegative: isNegative);
return u8aToHex(u8a, include0x: true);
}