Diffusion model

[henrikjacobsenfys]

Basic diffusion model. It's based off of the SampleModel branch since it creates SampleModels.

I've kept it a bit simpler than some of the other PRs in terms of allowed inputs, to get things flowing faster.

Once the overall structure is approved, I have ~6 more diffusion models to implement following the same style.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.19%. Comparing base (01b9490) to head (d251f22).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #60      +/-   ##
===========================================
+ Coverage    96.60%   98.19%   +1.59%     
===========================================
  Files           12       16       +4     
  Lines          412      775     +363     
===========================================
+ Hits           398      761     +363     
  Misses          14       14              

Flag	Coverage Δ
unittests	98.19% <100.00%> (+1.59%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[henrikjacobsenfys]

Would be nice to get this reviewed, but may make sense to wait until ComponentCollection has been merged to simplify things.