feat: add inflight task metrics to engine queue

[mikemillaa]

track inflight tasks by type in task queue

• Add ENGINE_INFLIGHT_TASKS gauge metric with task type labels
• Increment on enqueue, decrement on completion and queue clear
• Conditionally compiled with 'metrics' feature

Seeing occasional slowdowns during high load periods
but couldn't tell if it was build tasks backing up or derivation
falling behind. This gives us per-task-type visibility to identify
which part of the pipeline is the bottleneck.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.1%. Comparing base (c978d7c) to head (fb3e86c).
⚠️ Report is 84 commits behind head on main.

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[emhane]

can you pls add a grafana panel for this to the dashboard and a screenshot of that panel to the pe description

[mikemillaa]

can you pls add a grafana panel for this to the dashboard and a screenshot of that panel to the pe description

@emhane Thanks for the review! I've added the requested Grafana panel to the existing dashboard.

[github-actions]

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[mikemillaa]

@emhane @theochap Hi would you plz check this? In case this close

[theochap]

@emhane how does this PR look to you now? Is it good to merge?

[github-actions]

This pull request has been automatically marked as stale because it has been inactive for 3 weeks.
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[mikemillaa]

@theochap in case closing

[github-actions]

This pull request has been automatically marked as stale because it has been inactive for 3 weeks.
It will be closed in 1 week if no further activity occurs.
If you believe this PR should remain open, please add the M-prevent-stale label or leave a comment.

[mikemillaa]

@theochap

[github-actions]

This pull request has been automatically marked as stale because it has been inactive for 3 weeks.
It will be closed in 1 week if no further activity occurs.
If you believe this PR should remain open, please add the M-prevent-stale label or leave a comment.

[mikemillaa]

@emhane @theochap