Bug report

Bug description:

We have THREE different implementations for HMAC: one based on OpenSSL, one based on HACL* and a pure Python one that directly uses hash functions (HMAC can be written easily in Python if the hash function is given as input as well). Apart from that, we also a dispatching mechanism for "one-shot" HMAC that is a bit inconsistent:

• If OpenSSL is present -> we use OpenSSL's one-shot HMAC. The key and message sizes are limited to INT_MAX, otherwise an OverflowError occurs. If the algorithm doesn't exist, it falls back to HACL* if possible.
• HACL* implementations limits the key and message sizes to