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 95.23810% with 2 lines in your changes missing coverage. Please review.

Project coverage is 95.48%. Comparing base (315afca) to head (9ef72d5).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/event-handler.ts	94.87%	2 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@ ## main #1741 +/- ## ========================================== - Coverage 95.63% 95.48% -0.15%  ========================================== Files 92 93 +1 Lines 5195 5205 +10 Branches 879 564 -315 ========================================== + Hits 4968 4970 +2  - Misses 227 235 +8 

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