Introduce a dedicated class for handling hexadecimal numbers or use an existing one if available, rather than using strings

[boorich]

[sneakzttv]

Currently we're using strings as hex in some places and other places we're using nethereum's hex type. We should be changing everything to use nethereum's type so that we achieve uniformity across the board. As well as checking that everything functions as intended.

[sneakzttv]

This has been rectified due to recent updates.