speed up and other improvements

[gaelforget]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 95.83333% with 1 line in your changes missing coverage. Please review.

Project coverage is 92.30%. Comparing base (19bc860) to head (49d9333).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
src/Integration.jl	95.83%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #150      +/-   ##
==========================================
+ Coverage   92.24%   92.30%   +0.06%     
==========================================
  Files          22       22              
  Lines        2670     2691      +21     
==========================================
+ Hits         2463     2484      +21     
  Misses        207      207              

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