Backport of api: fix allocation stats to exclude non running tasks from usage into release/1.11.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #27317 to be assessed for backporting due to the inclusion of the label backport/1.11.x.

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

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Description

That allocation stats endpoint should not include stats from non running/completed tasks in it's current resource usage metrics. These changes exclude adding the latest stats if the task is not running.

Testing & Reproduction steps

Run a job with a prestart task that takes a lot of CPU or memory (ex. stress-ng). Have main task sleep. See that allocation resource usage is still very high.

Links

Fixes #27294

Contributor Checklist

• Changelog Entry If this PR changes user-facing behavior, please generate and add a
  changelog entry using the make cl command.
• Testing Please add tests to cover any new functionality or to demonstrate bug fixes and
  ensure regressions will be caught.
• Documentation If the change impacts user-facing functionality such as the CLI, API, UI,
  and job configuration, please update the Nomad product documentation, which is stored in the
  web-unified-docs repo. Refer to the web-unified-docs contributor guide for docs guidelines.
  Please also consider whether the change requires notes within the upgrade
  guide. If you would like help with the docs, tag the nomad-docs team in this PR.

Reviewer Checklist

• Backport Labels Please add the correct backport labels as described by the internal
  backporting document.
• Commit Type Ensure the correct merge method is selected which should be "squash and merge"
  in the majority of situations. The main exceptions are long-lived feature branches or merges where
  history should be preserved.
• Enterprise PRs If this is an enterprise only PR, please add any required changelog entry
  within the public repository.

• If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

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Overview of commits

• 52629ac