Detect use of felt252 operations with tainted parameters

[technovision99]

Reports if a felt252 binary operation is used, including the tainted parameters if it is. Also skips analyzing the contractState parameter in external functions since this caused every use of a storage variable to appear tainted.

Known FPs:
Something like a+b+c will get flagged twice since the code gets translated into two additions at the Sierra level
Any equality comparison a == b will get flagged since the code gets translated to felt252_is_zero(felt252_sub(a,b))