The hidden-window sweep built a Vec of cloned Window handles purely to
work around the borrow checker: unmap_elem needs &mut self.space while
the iteration borrows self.window_ids. Move the space out with
mem::take instead and unmap in place, dropping the allocation and the
per-window clone.
Behaviour is unchanged. unmap_elem only removes the element passed to
it, so it cannot affect element_location for any other window, which
makes checking each window immediately before its own unmap equivalent
to testing every hidden window up front; the unmap order is the same
window_ids iteration order. The |= is deliberate so the check never
short-circuits past an unmap.
This is a cleanup, not a measured win. The sweep is dominated by the
linear scans inside element_location and unmap_elem, and a Vec only
allocated when windows were actually hidden, so the saving is small.
Verified with twelve live foot windows across forty workspace switches.
Samuel Onoja
7d3a88bef7