pub fn with_capacity(capacity: usize) -> Self {
        Self {
            local: Vec::with_capacity(capacity),
            inner: T::InnerRegion::default(),
        }
    }
Construct a [TimelyStack], reserving space for `capacity` elements

Note that the associated region is not initialized to a specific capacity
because we can't generally know how much space would be required.
differential-dataflow/src/containers.rs