Add more logging in vtgate buffering - ensureConsistentLocked (#771)

[tanjinx]

Description

Related Issue(s)

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

Deployment Notes

AI Disclosure

[codecov-commenter]

Codecov Report

❌ Patch coverage is 54.54545% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.74%. Comparing base (b1ab347) to head (17c75c8).
⚠️ Report is 24 commits behind head on slack-22.0.

Files with missing lines	Patch %	Lines
go/vt/discovery/keyspace_events.go	54.54%	5 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##           slack-22.0     #781      +/-   ##
==============================================
+ Coverage       67.53%   69.74%   +2.21%     
==============================================
  Files            1600     1605       +5     
  Lines          261782   213571   -48211     
==============================================
- Hits           176786   148950   -27836     
+ Misses          84996    64621   -20375     

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.