Construct a BigInt from a decimal or hexadecimal string. The number must
be in the form of a decimal or hex literal. It may have a leading +
or - sign, followed by 0x or 0X if hexadecimal. Underscores are
permitted in any location after the 0x and/or the sign of the number.
Construct a BigInt from a decimal or hexadecimal string. The number must be in the form of a decimal or hex literal. It may have a leading + or - sign, followed by 0x or 0X if hexadecimal. Underscores are permitted in any location after the 0x and/or the sign of the number.