refactor(capi): use RwLock to replace mut static reference

[kanru]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.

Project coverage is 89.84%. Comparing base (2a356df) to head (7bf5652).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
capi/src/io.rs	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #663      +/-   ##
==========================================
- Coverage   89.85%   89.84%   -0.01%     
==========================================
  Files          42       42              
  Lines        8789     8777      -12     
==========================================
- Hits         7897     7886      -11     
+ Misses        892      891       -1     

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