Fix #4183: Adjust Overall Performance runtime in HTML test report

[Vaibhavsahu2810]

Description

This pull request addresses issue #4183, where the Overall Performance runtime displayed in the Nightwatch HTML report differed from the Suite runtime for single-suite runs. The discrepancy arose due to differing calculation methods for these runtime metrics, causing confusion for users analyzing test execution data.

Changes Made

Updated the aggregateStats Method:
The method now calculates the Overall Performance runtime by summing the actual execution times (timeMs) of test cases instead of relying solely on start and end timestamps.

Proof of Work

The report shows consistent runtimes across sections for both Overall Performance and Suite runtime.

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[garg3133]

@Vaibhavsahu2810 Thanks for this PR. But, were you able to figure out why the subtraction of the above two variables is giving the wrong time?

Ideally, we should try to find the root cause of the problem and try to tackle that instead of just introducing a fix. If the this.results.endTimestamp is wrong above, we should fix that because it might be causing problems at other places as well.

Also, if the tests are running in parallel, we wouldn't just want to add up the time of all the tests but instead show the time the entire test run actually took from the user's perspective (if I'm not missing something here?).