fix(metrics): prevent negative utilization values

[pront]

Summary

100% LLM generated. Use at your own risk.

I didn't want to just clamp and hide the root cause.

Vector configuration

How did you test this PR?

Change Type

• Bug fix
• New feature
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the no-changelog label to this PR.

References

closes: #24060

Notes

• Please read our Vector contributor resources.
• Do not hesitate to use @vectordotdev/vector to reach out to us regarding this PR.
• Some CI checks run only after we manually approve them.
  • We recommend adding a pre-push hook, please see this template.
  • Alternatively, we recommend running the following locally before pushing to the remote branch:
    • make fmt
    • make check-clippy (if there are failures it's possible some of them can be fixed with make clippy-fix)
    • make test
• After a review is requested, please avoid force pushes to help us review incrementally.
  • Feel free to push as many commits as you want. They will be squashed into one before merging.
  • For example, you can run git merge origin master and git push.
• If this PR introduces changes Vector dependencies (modifies Cargo.lock), please
  run make build-licenses to regenerate the license inventory and commit the changes (if any). More details here.

[bruceg]

I don't see any major problems in the code as it stands, but I don't have a great understanding of the conditions under which it can go negative in the first place which makes me nervous that this change is just papering over a larger bug. I have some suggestions for cleanups below.

[pront]

Cleaned up the PR based on code review comments.

but I don't have a great understanding of the conditions under which it can go negative in the first place which makes me nervous that this change is just papering over a larger bug

Same concern here. Will need to spend more time digging through the code.