Update output message timestamping.

[umaannamalai]

This PR updates timestamping on LLM events representing output messages so that they keep the timestamp that is added once the custom event is ready to be recorded.

[github-actions]

✅MegaLinter analysis: Success

Descriptor	Linter	Files	Fixed	Errors	Warnings	Elapsed time
✅ ACTION	actionlint	7		0	0	0.93s
✅ MARKDOWN	markdownlint	7	0	0	0	1.29s
✅ PYTHON	ruff	960	0	0	0	1.04s
✅ PYTHON	ruff-format	960	0	0	0	0.32s
✅ YAML	prettier	15	0	0	0	1.42s
✅ YAML	v8r	15		0	0	6.08s
✅ YAML	yamllint	15		0	0	0.65s

See detailed reports in MegaLinter artifacts

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.68%. Comparing base (a7ade08) to head (8a76a2a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1627      +/-   ##
==========================================
+ Coverage   81.65%   81.68%   +0.02%     
==========================================
  Files         209      209              
  Lines       24392    24384       -8     
  Branches     3870     3866       -4     
==========================================
- Hits        19918    19917       -1     
+ Misses       3162     3159       -3     
+ Partials     1312     1308       -4     

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