Provide example to calculate mu for ML-DSA

[mschulz-at-hilscher]

It would be nice to have some example code for calculating mu.

I wrote the attached one, which is inspired by https://github.com/nsmithuk/mldsa-mu-py/blob/main/src/mldsa_mu/mu.py.

I first generate a signature, then i generate mu manually and verify the signature using verify_mu. Then I also generate a hashmldsa signature and verify it using openssl (taken from wsl in my example).

hashmldsa.py

[alex]

We'd like to provide an incremental API for computing these -- there's not much point in computing external mu with the entire message in memory (if you could do that, you can just pass the whole thing to sign!)

[mschulz-at-hilscher]

The first step was just to verify that the mu calculation works. The second part is the more interesting part for me where I use mu to sign and verify hashmldsa signatures.
One could provide the example on how to calculate mu to work with hashmldsa signatures.
I just wanted to share the program for anyone who likes to perform hashmldsa operations with python cryptography.