Fix: Relax soma/first point check

[arnaudon]

If one has a soma located far from origin, the rtol may consider the point to be too close, hence its better to only use atol.

[codecov[bot]]

Codecov Report

Merging #68 (f77efda) into main (d4d5ecb) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main      #68   +/-   ##
=======================================
  Coverage   97.57%   97.57%           
=======================================
  Files          39       39           
  Lines        2148     2148           
  Branches      330      330           
=======================================
  Hits         2096     2096           
  Misses         35       35           
  Partials       17       17           

Flag	Coverage Δ
pytest	97.57% <100.00%> (ø)

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Impacted Files	Coverage Δ
neurots/generate/soma.py	100.00% <100.00%> (ø)