More extensible effect notification about signia

[ds300]

Thanks for the great suggestion!

I see the value and I think it would work well for EffectScheduler.

Computed is a bit trickier

• Making traverse polymorphic could impact perf since it is used in such hot loops. But it could also be fine 🤷‍♀️
• It would bake in the current graph traversal approach and might make it difficult to add perf improvements or new features over time, e.g. I don't think push nodes would work implemented this way, they required a few extra core changes, and even then they weren't working 100% correctly according to the fuzz tests.

I'd be happy to merge a PR enabling this for EffectScheduler via an extra callback arg! That feels like a minimal and sensible change that provides a lot of extra leverage.

[justjake]

Agree about baking in the tree traversal 👍🏻, it's certainly a stretch to consider that polymorphism; going that route would need a lot more design.