Update doctest with few modifications.

[MFraters]

Small changes to the doctest, based on the review in the doctest repository. Will most likely keep this open and update it until the pull request there is merged.

[codecov]

Codecov Report

Merging #393 (11f6011) into main (56e20c6) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #393   +/-   ##
=======================================
  Coverage   99.00%   99.00%           
=======================================
  Files          79       79           
  Lines        4711     4711           
=======================================
  Hits         4664     4664           
  Misses         47       47           

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[github-actions]

Benchmark	Main	Feature	Difference (99.9% CI)
Slab interpolation simple none	1.438 ± 0.028 (s=303)	1.440 ± 0.030 (s=325)	-0.4% .. +0.7%
Slab interpolation curved simple none	1.495 ± 0.040 (s=311)	1.496 ± 0.037 (s=293)	-0.6% .. +0.8%
Spherical slab interpolation simple none	1.776 ± 0.015 (s=271)	1.775 ± 0.014 (s=238)	-0.3% .. +0.2%
Slab interpolation simple curved CMS	1.738 ± 0.134 (s=283)	1.736 ± 0.054 (s=238)	-1.8% .. +1.6%
Spherical slab interpolation simple CMS	2.437 ± 0.048 (s=192)	2.447 ± 0.052 (s=179)	-0.3% .. +1.1%
Spherical fault interpolation simple none	1.481 ± 0.007 (s=314)	1.481 ± 0.007 (s=296)	-0.1% .. +0.1%