Rework diffusion models

[henrikjacobsenfys]

The changes are described here: #190

I'm missing some tests, but the code is more or less how I want it to be, so a review would be nice

[codecov]

Codecov Report

❌ Patch coverage is 88.22055% with 47 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.27%. Comparing base (fff0285) to head (636693c).

Files with missing lines	Patch %	Lines
...mics/sample_model/diffusion_model/delta_lorentz.py	90.49%	18 Missing and 5 partials ⚠️
...mple_model/diffusion_model/diffusion_model_base.py	79.38%	16 Missing and 4 partials ⚠️
src/easydynamics/analysis/fit_binding.py	0.00%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #191      +/-   ##
===========================================
- Coverage    98.42%   97.27%   -1.15%     
===========================================
  Files           50       51       +1     
  Lines         3175     3524     +349     
  Branches       576      649      +73     
===========================================
+ Hits          3125     3428     +303     
- Misses          26       62      +36     
- Partials        24       34      +10     

Flag	Coverage Δ
integration	44.97% <35.33%> (-1.20%)	⬇️
unittests	97.16% <87.21%> (-1.27%)	⬇️

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