[release-19.0]: VTOrc optimize TMC usage (#15356)

[GuptaManan100]

Description

This is a backport of #15356

Related Issues

As described in #15726 (comment), this backport is required to fix the bug #15726.

• Fixes Bug Report: vtorc Client received GoAway with error code ENHANCE_YOUR_CALM and debug data equal to ASCII "too_many_pings" #15726

[vitess-bot]

Review Checklist

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• vtctl command output order should be stable and awk-able.

[GuptaManan100]

I have verified manually, this change is fixing the memory leak in #15726

[codecov]

Codecov Report

Attention: Patch coverage is 1.75439% with 56 lines in your changes are missing coverage. Please review.

Project coverage is 67.43%. Comparing base (e60fbd7) to head (8ca5f00).

Files	Patch %	Lines
go/vt/vtorc/inst/instance_dao.go	0.00%	43 Missing ⚠️
go/vt/vtorc/logic/topology_recovery.go	16.66%	5 Missing ⚠️
go/vt/vtorc/inst/tablet_dao.go	0.00%	4 Missing ⚠️
go/vt/vtorc/logic/tablet_discovery.go	0.00%	3 Missing ⚠️
go/vt/vttablet/grpctmclient/client.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##           release-19.0   #15759   +/-   ##
=============================================
  Coverage         67.43%   67.43%           
=============================================
  Files              1560     1560           
  Lines            192765   192760    -5     
=============================================
+ Hits             129991   129997    +6     
+ Misses            62774    62763   -11     

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[deepthi]

I'm curious about the codecov report. Looks like all this code is actually covered by e2e tests, but not unit tests?

[GuptaManan100]

Yes exactly!