fix: Calculate first and last timestamps from raw data

[metal-messiah]

Ensure the agent manually calculates the first and last timestamps of a SessionReplay payload before harvesting to help improve consistency on the UI replayer.

Overview

Related Issue(s)

https://new-relic.atlassian.net/browse/NR-428135?atlOrigin=eyJpIjoiNWZiYmZjM2UxMDJkNDQyMzg3ZDVkOGMxOWFmZDkwYzEiLCJwIjoiaiJ9

Testing

new unit test has been added to validate the new method.

[github-actions]

Supportability Metric Usage Changes:

No matching changes found

Supportability Metrics .md File Changes:

supportability_metrics.md was changed? false

New supportability metrics require changes to supportability_metrics.md, as well as a new PR to Angler. Please ensure an Angler PR is created and linked to this PR.

[github-actions]

Asset Size Report

Merging this pull request will result in the following asset size changes:

Agent	Asset	Previous Size	New Size	Diff
lite	loader	25.57 kB / 9.64 kB (gzip)	25.57 kB / 9.64 kB (gzip)	0% / 0% (gzip)
lite	async-chunk	54.16 kB / 17.89 kB (gzip)	54.16 kB / 17.89 kB (gzip)	0% / 0% (gzip)
pro	loader	53.74 kB / 18.88 kB (gzip)	53.74 kB / 18.88 kB (gzip)	0% / -0.03% (gzip)
pro	async-chunk	92.72 kB / 28.71 kB (gzip)	93.03 kB / 28.81 kB (gzip)	0.34% / 0.33% (gzip)
spa	loader	62.5 kB / 21.6 kB (gzip)	62.5 kB / 21.6 kB (gzip)	0% / 0% (gzip)
spa	async-chunk	117.3 kB / 35.7 kB (gzip)	117.61 kB / 35.78 kB (gzip)	0.27% / 0.24% (gzip)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.80%. Comparing base (42a16ee) to head (d38ec9c).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1535   +/-   ##
=======================================
  Coverage   87.79%   87.80%           
=======================================
  Files         198      198           
  Lines        7808     7814    +6     
  Branches     1573     1576    +3     
=======================================
+ Hits         6855     6861    +6     
  Misses        822      822           
  Partials      131      131           

Flag	Coverage Δ
unit-tests	79.10% <100.00%> (+0.02%)	⬆️

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[github-actions]

Last ran on July 30, 2025 12:24:15 CDT
Checking merge of (24a2ba3) into main (42a16ee)

[ellisong]

see comment

[ptang-nr]

LGTM