Hex bug fix

[harisang]

This PR fixes some minor bug introduced in PR #31 with the conversion of Hex Bytes to strings and vice versa.

[bram-vdberg]

Do we need to apply this change to the whole project? I see we use the .hex() method in a few other files as well.

[shubhagarwal03]

I'll check to see if its needed in other files, but I believe the rest of the codebase is as is, and had no issues in the prev deployment.

[fhenneke]

There is one conversion to to_0x_hex missing in the get_order_data function.

Some of the other uses are for use in other methods of the package. Some of the should handle strings without 0x prefix correctly. But probably worth double checking.

[harisang]

Yeah good catch, just pushed the fix for the get_order_data() function. Getting rate limited again so will wait to test it locally before merging.