Check `as_int` calls using `to_bigint` instead of `to_signed_felt` in hint implementationss

[fmoletta]

In a previous iteration, the logic of the function as_int was implemented in the felt library under the to_bigint method. Later on, the to_bigint was changed to be just a simple type conversion, and the as_int logic was moved to the to_signed_felt method. Nevertheless, some hints are still using to_bigint when they should be using to_signed_felt (example #1189).
All hints using as_int in their python code should be checked to make sure we using to_signed_felt on their implementation