Fix stats beat failure count metrics reporting incorrect values

[jeanbisutti]

Fix bugs related to stats beat read and write failure count.

[Copilot]

Pull request overview

This PR fixes critical bugs in the statsbeat failure count metrics reporting where incorrect values were being sent to telemetry. The bugs were caused by using the wrong variables when creating telemetry items - the code was reading from atomic counters after they had been reset instead of using the captured values, and there was a copy-paste error where readFailureCount was used instead of writeFailureCount.

Changes:

• Fixed three bugs in NonessentialStatsbeat.send() method that caused incorrect metric values to be reported
• Added comprehensive test coverage to verify the fixes and prevent regression

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
NonessentialStatsbeat.java	Fixed bugs on lines 38, 42, and 45: using captured values instead of re-reading atomic counters, and correcting copy-paste error where readFailureCount was used instead of writeFailureCount
NonessentialStatsbeatTest.java	Added three new test methods to verify correct metric values are sent and counters are properly reset after sending