[Ada] Navigate to next node in bucket when iterating

There are two overloadings of Next. One is a selector function to return the next node in the current bucket, the other navigates to the next element in the container. The implementation of Generic_Iteration needs to call the former, as it interrogates the items in each bucket, before moving on the

[Ada] Navigate to next node in bucket

There are two overloadings of Next. One is a selector function to return the next node in the current bucket, the other navigates to the next element in the container. The implementation of Generic_Equal needs to call the former, as it interrogates the items in each bucket. Also, the buckets array