Make circular attributes thread safe

[cacay]

No description provided.

[codecov]

Codecov Report

Merging #364 (6371121) into master (fb8ac65) will increase coverage by 0.00%.
The diff coverage is 89.28%.

@@            Coverage Diff            @@
##             master     #364   +/-   ##
=========================================
  Coverage     59.58%   59.59%           
  Complexity     1133     1133           
=========================================
  Files           234      234           
  Lines          9085     9087    +2     
  Branches       1362     1362           
=========================================
+ Hits           5413     5415    +2     
  Misses         3409     3409           
  Partials        263      263           

Impacted Files	Coverage Δ
...du/cornell/cs/apl/attributes/CircularAttributes.kt	83.63% <89.28%> (+0.61%)	⬆️

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