Add Integer parsing helpers for Objo hex and binary strings

Add shared Integer methods that parse hexadecimal and binary text using Objo literal syntax, so runtime strings can be converted consistently with source-code literals.

For example, Integer.FromHex("0xFF") should return 255, and Integer.FromBinary("0b1010") should return 10. Values can then be assigned to Double variables through the existing Integer-to-Double widening.