Fix the behavior of setCount in UnionFindSet when used concurrently

[jjppp]

The UnionFindSet is used concurrently in algorithms such as Mahjong and DFAEquivChecker. However, UnionFind is not thread-safe since the setCount variable in the UnionFindSet class is simply int instead of AtomicInteger.

This PR fixes the bug above by converting the type of setCount from int to AtomicInteger.

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Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 71.93%. Comparing base (a8b3982) to head (bfb5b21).

Files with missing lines	Patch %	Lines
...java/pascal/taie/util/collection/UnionFindSet.java	0.00%	4 Missing ⚠️

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Additional details and impacted files

@@             Coverage Diff              @@
##             master     #147      +/-   ##
============================================
- Coverage     71.95%   71.93%   -0.02%     
  Complexity     4365     4365              
============================================
  Files           479      479              
  Lines         15868    15869       +1     
  Branches       2179     2179              
============================================
- Hits          11418    11416       -2     
- Misses         3570     3574       +4     
+ Partials        880      879       -1     

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[jjppp]

I have read the CLA Document and I hereby sign the CLA