[Request]: Helper function for hashing bound authorization token

### Contact Details

erik.blucher@eletive.com

### Is your feature request related to a problem?

Both resource servers and clients needs to hash bound authorization tokens during a normal DPoP authorization flow. If done incorrectly on either side it will result in a `ath` mismatch.

### A clear and concise description of what you want to happen.

It would be helpful if the dpop-package had a utility function to hash a token according to the specification. Then both clients and resource servers could be confident in that the hash is made according to specification and reduce likelihood that a `ath` mismatch will occur.

### Additional Notes

_No response_

### Code of Conduct

- [X] I agree to follow this project's Code of Conduct

The issue names no files or tests. Start by locating existing DPoP token and ath handling in the Go package, then compare it with the specification’s hashing requirements. Done means clients and resource servers can use one utility and produce matching ath values.

Written by the indexing model from the issue text.