feat: testOnly events

[mdjastrzebski]

Summary

Resolves #1738

Provides support for testOnly_onXxx events to Fire Event and User Event, which together with software-mansion/react-native-gesture-handler#3357 allow for RNGH Pressable to work with RNTL.

Test plan

Addent automatic tests. Validate after RNGH PR is merged and published.

CC: @latekvo @sidferreira

[codecov]

Codecov Report

Attention: Patch coverage is 95.12195% with 2 lines in your changes missing coverage. Please review.

Project coverage is 95.55%. Comparing base (17ccd9e) to head (53ef89d).

Files with missing lines	Patch %	Lines
src/event-handler.ts	94.73%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1741      +/-   ##
==========================================
+ Coverage   95.50%   95.55%   +0.04%     
==========================================
  Files          92       93       +1     
  Lines        5139     5148       +9     
  Branches      563      564       +1     
==========================================
+ Hits         4908     4919      +11     
+ Misses        231      229       -2     

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