fix(summary.sim): obtain confint length correctly

[benesom]

No description provided.

[benesom]

the fix is [[1]], which is required to obtain a vector such that mean() works as expected.

[codecov]

Codecov Report

❌ Patch coverage is 92.30769% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 73.56%. Comparing base (8b2d650) to head (25dfe35).
⚠️ Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
R/sim.default.R	92.30%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #20      +/-   ##
===========================================
+ Coverage    73.54%   73.56%   +0.01%     
===========================================
  Files          164      164              
  Lines        15209    15216       +7     
===========================================
+ Hits         11186    11193       +7     
  Misses        4023     4023              

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