add a few performance test

[lkzhao]

No description provided.

[codecov-io]

Codecov Report

Merging #120 into master will increase coverage by 0.08%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #120      +/-   ##
==========================================
+ Coverage   73.46%   73.55%   +0.08%     
==========================================
  Files          41       41              
  Lines        1123     1123              
==========================================
+ Hits          825      826       +1     
+ Misses        298      297       -1

Impacted Files	Coverage Δ
Sources/Layout/SimpleLayout.swift	78.26% <0%> (+2.17%)	⬆️

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