Move epsilon parameter in MorphRGrid

[Sparks29032]

The intent of epsilon is to ensure that the rmax point is excluded. By setting epsilon = rstep/2, we ensure that only that last point is excluded, even on denser grids (i.e. grids denser than rstep=1e-08).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.12%. Comparing base (c4eba1e) to head (cfaa83b).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #242   +/-   ##
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  Coverage   99.12%   99.12%           
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  Files          21       21           
  Lines        1142     1142           
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  Hits         1132     1132           
  Misses         10       10           

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