VReplication: Improve error handling in VTGate VStreams

[mattlord]

Description

Related Issue(s)

• Fixes: Feature Request: Improve VStream Error Messages #17548

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

• Ensure that the Pull Request has a descriptive title.
• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

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Documentation

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Backward compatibility

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[codecov]

Codecov Report

Attention: Patch coverage is 43.10345% with 33 lines in your changes missing coverage. Please review.

Project coverage is 67.70%. Comparing base (71ccd6d) to head (a136b86).

Files with missing lines	Patch %	Lines
go/vt/vtgate/vstream_manager.go	43.10%	33 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17558      +/-   ##
==========================================
- Coverage   67.71%   67.70%   -0.01%     
==========================================
  Files        1584     1584              
  Lines      254721   254741      +20     
==========================================
+ Hits       172473   172479       +6     
- Misses      82248    82262      +14     

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