Port `pathfinder`'s Pedersen hash performance improvements

[xJonathanLEI]

The Pedersen hash implementation added by #33 was refactored from b091cb8 @ pathfinder. Changes have been made to their implementation that they claim to offer a 10x performance improvement.

[xJonathanLEI]

Just ran their benchmark on my machine.

Before (b091cb8):

pedersen_hash           time:   [3.1228 ms 3.1455 ms 3.1732 ms]

After (3331f26):

pedersen_hash           time:   [239.06 us 240.10 us 241.21 us]