feat: thread safe

[duduWang20]

#311

[codecov-io]

Codecov Report

Merging #312 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #312      +/-   ##
==========================================
+ Coverage   99.28%   99.28%   +<.01%     
==========================================
  Files           2        2              
  Lines        1540     1548       +8     
==========================================
+ Hits         1529     1537       +8     
  Misses         11       11

Impacted Files	Coverage Δ
YYModel/NSObject+YYModel.m	99.22% <100%> (ø)	⬆️
YYModel/YYClassInfo.m	99.62% <100%> (ø)	⬆️

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