update single-cell notebook with trajectories from a given cell

[kilianFatras]

What does this PR do?

This PR adds illustration examples to the single-cell notebooks where we show the trajectory difference between SF2M and SBCFM from the same cell. SB-CFM only produces one trajectory (by its deterministic nature) contrary to SF2M which produces several outputs as it models a stochastic process.

It is a novel feature.

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Codecov Report

All modified lines are covered by tests ✅

Comparison is base (dbeeb75) 34.23% compared to head (64aed61) 34.23%.
Report is 2 commits behind head on main.

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Additional details and impacted files

@@           Coverage Diff           @@
##             main      #64   +/-   ##
=======================================
  Coverage   34.23%   34.23%           
=======================================
  Files          55       55           
  Lines        6268     6268           
=======================================
  Hits         2146     2146           
  Misses       4122     4122           

Files	Coverage Δ
runner/src/datamodules/distribution_datamodule.py	44.82% <100.00%> (ø)
runner/src/eval.py	81.08% <ø> (ø)
runner/src/train.py	92.59% <ø> (ø)

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[atong01]

LGTM