Support `.for_each` inside a tick

[shadaj]

Should be easy to implement, just need to do .all_ticks on the user's behalf.

[ydewit]

I’m trying to wrap my head around this issue. I see there’s already a for_each() implementation for streams that are not in a Tick:

impl<'a, T, L, B, O> Stream<T, L, B, O>
where
    L: Location<'a> + NoTick,

The goal seems to be to enable users to call .for_each() on streams inside a Tick.

The most straightforward change would be to simply allow .for_each() in Tick locations as well. However, I have a couple of questions:

• I don’t yet understand what the Unpersist node does. Does it free all state Persisted in the current tick, or all state persisted so far?
• I don’t see a NoAtomic bound in the current .for_each() implementation. I’m assuming this is just an oversight and that I just need to enable .for_each() in all locations. Or is there a specific node that needs to be added to “free” the atomic block?