Fix excessive CPU usage

[Miksus]

No description provided.

[codecov-commenter]

Codecov Report

Merging #43 (f410b7e) into master (420210f) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #43      +/-   ##
==========================================
+ Coverage   90.06%   90.08%   +0.02%     
==========================================
  Files          81       81              
  Lines        3652     3652              
==========================================
+ Hits         3289     3290       +1     
+ Misses        363      362       -1     

Impacted Files	Coverage Δ
rocketry/session.py	87.65% <100.00%> (ø)
rocketry/core/schedule.py	89.78% <0.00%> (+0.36%)	⬆️

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