Fixed critical bug in PATCH API calls & improved error reporting

[sudosammy]

The library was unable to make PATCH API calls in line with current Wise API requirements. This prevents is from being able to make serveral API calls in Staging and Prod, including required calls for: https://docs.wise.com/api-docs/api-reference/batch-group payments.

Additionally, the library's error handling was failing on certain API calls, so I make this more robust.

I also added specific error handling for One Time Token reasons: https://docs.wise.com/api-docs/api-reference/one-time-token

I also added the ability to modify the headers that are sent to the Wise API (which was ultimately the issue leading to the failing PATCH requests).

This is all backwards compatible.