Backport of client: Use single time variable when handling heartbeat response. into release/1.10.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #26238 to be assessed for backporting due to the inclusion of the label backport/1.10.x.

The below text is copied from the body of the original PR.

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When the client handles an update status response from the server, it modifies its heartbeat stop tracker with a time set once the RPC call returns. It optionally also emits a log message, if the client suspects it has missed a heartbeat.

These times were originally tracked by two different calls to the time function which were executed 2 microseconds apart. There is no reason we cannot use a single time variable for both uses which saves us one whole call to time.Now.

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Overview of commits

• 7c5a578