[WIP] Uncertainty POC for MrVI

[PierreBoyeau]

solves #21

[codecov]

Codecov Report

Merging #11 (6875d87) into main (1eced8f) will decrease coverage by 0.46%.
The diff coverage is 96.66%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #11      +/-   ##
==========================================
- Coverage   98.67%   98.20%   -0.47%     
==========================================
  Files           6        6              
  Lines         302      391      +89     
==========================================
+ Hits          298      384      +86     
- Misses          4        7       +3     

Flag	Coverage Δ
unittests	98.20% <96.66%> (-0.47%)	⬇️

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Impacted Files	Coverage Δ
src/scvi_v2/_model.py	98.31% <96.66%> (-1.69%)	⬇️