[release-19.0] parse transaction timeout as duration (#16338)

[mattlord]

Description

This is a manual backport of #16338

[vitess-bot]

Review Checklist

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General

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 65.12%. Comparing base (8d6953d) to head (cef5a47).
Report is 1 commits behind head on release-19.0.

Files with missing lines	Patch %	Lines
go/vt/vttest/vtprocess.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##           release-19.0   #17406   +/-   ##
=============================================
  Coverage         65.12%   65.12%           
=============================================
  Files              1560     1560           
  Lines            238305   238305           
=============================================
+ Hits             155186   155205   +19     
+ Misses            83119    83100   -19     

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