fix: builtin transformer should keep the keys

[KeranYang]

fixes #2043

[codecov]

Codecov Report

Attention: Patch coverage is 93.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 63.23%. Comparing base (24c6553) to head (387bf99).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...n/time_extraction_filter/time_extraction_filter.go	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2047      +/-   ##
==========================================
- Coverage   63.38%   63.23%   -0.16%     
==========================================
  Files         319      319              
  Lines       29171    29171              
==========================================
- Hits        18491    18445      -46     
- Misses       9665     9717      +52     
+ Partials     1015     1009       -6     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.