MvNormalWishart node implementation

[esther-van-pelt]

This node exposes the Multivariate Normal-Wishart distribution which can be constructed with PointMass inputs.

[wouterwln]

LGTM!

[github-actions]

🤖 Code Formatting

Your PR still has some code formatting issues. I've updated PR #566 with the necessary formatting changes.

You can merge that PR into this branch to fix the code style check.

Alternatively, you can run make format locally and push the changes yourself.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.28%. Comparing base (d2c8dde) to head (e028206).
⚠️ Report is 30 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #565      +/-   ##
==========================================
+ Coverage   80.23%   80.28%   +0.04%     
==========================================
  Files         211      211              
  Lines        6189     6265      +76     
==========================================
+ Hits         4966     5030      +64     
- Misses       1223     1235      +12     

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