refcell

* **#9445** 👈 * `develop` This stack of pull requests is managed by Graphite. Learn more about stacking. Join @refcell and the rest of your teammates on Graphite

Closing in favor of #9890

Current dependencies on/for this PR: * `develop` * **PR #9324** 👈 This [stack of pull requests](https://stacking.dev/?utm_source=stack-comment) is managed by [Graphite](https://app.graphite.dev/github/pr/ethereum-optimism/optimism/9324?utm_source=stack-comment).

Will continue to work in this branch to extend the scheduler abstraction to the top level `Scheduler`

> lgtm. it'll be useful to add a "drain" function to the scheduler. Since there could be pending tasks that may not get run after Close. This is a good...

There's a bug here whereby there is contention on the `cancel` between the spawned goroutine and the `Close` method. Need to work through that. Open to suggestions.

Hey @protolambda, tacking on the https://github.com/ethereum-optimism/optimism/labels/S-exempt-stale label on here so you don't need to constantly remove https://github.com/ethereum-optimism/optimism/labels/Stale

> Not opposed to the comments being broken out into their own PR Will do going forward - keeping for now as i'm still learning.

> How would you harden the existing shuffling function? Scratch that 😅

Implemented by the 🐐 @MathisGD in #89