chore: create bench dir

[hasundue]

• fix(testing): implement onXXX methods in MockWebSocket
• refactor(lib/websockets)!: abandon first and get instances
• refactor(lib/testing): MockWebSocket.instances now returns AsyncGenerator
• chore: create bench dir

[codecov]

Codecov Report

Attention: Patch coverage is 88.37209% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 86.75%. Comparing base (b8e3af6) to head (9ccb58d).

Files	Patch %	Lines
lib/testing.ts	88.37%	4 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #36      +/-   ##
==========================================
+ Coverage   86.22%   86.75%   +0.53%     
==========================================
  Files          22       22              
  Lines         704      725      +21     
  Branches       43       52       +9     
==========================================
+ Hits          607      629      +22     
  Misses         95       95              
+ Partials        2        1       -1     

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