feat: add Stack empty

[mattsse]

Adds a helper function to get an empty Stack.

this can be beneficial during tracing where stack capturing is optional, and working with Stack over Option<Stack> is preferred

ref paradigmxyz/reth#5521

[rakita]

cc #816 as this stack is going to be overwritten.

[rakita]

Wait, this would make functions invalid in Stack as they depend on STACK_LIMIT, so best not to include this.

[rakita]

Additionally, I think you should just clone the stack slice as they have separate purpose that don't overlap, and when a shared stack comes this is going to be needed.

[mattsse]

Wait, this would make functions invalid in Stack as they depend on STACK_LIMIT, so best not to include this.

ah because the memory operations would be invalid, like ptr based copies? which require capacity?

makes sense, but then this type should not be Clone

[gbrew]

Wait, this would make functions invalid in Stack as they depend on STACK_LIMIT, so best not to include this.

ah because the memory operations would be invalid, like ptr based copies? which require capacity?

makes sense, but then this type should not be Clone

Yeah, I was just looking at this, and I agree the #[derive(Clone)] on Stack is unsafe, as it won't preserve the invariant that the stack is fully allocated.