Box futures passed to block_on in debug mode

[ibraheemdev]

Tokio currently does this in spawn but not block_on. For large async main functions this can lead to stack overflows in debug mode, especially on Windows. See astral-sh/uv#4851 for example.

[mox692]

I think we can add similar checks for block_on as well.

@Darksonn
Do you have a better idea other than just adding Future's size check logic like #4009? (I'm wondering since it seems that you said such a possibility in that PR.)

[Darksonn]

There are some other approaches, but they are more complicated. Basically, the idea is to avoid passing the future by ownership through many function calls. Instead, you create a kind of owned pointer that references the future object on the stack, and then you pass the pointer all the way down to the function that moves it to the heap.

But I'm happy to add a size check for now.