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fix(cseMachine): don't prune a frame that's still a closure's home (#4380) (#4381)

isEmptyEnvironment-based frame collapsing (getNextChildren, and
getVisibleChildren under clear-dead-frames) treated any bindingless
frame as boring and safe to hide, without checking whether it's still
the defining environment of a live closure or array elsewhere (stash,
control, or another frame's bindings). When it was — e.g. a bare
top-level `lambda x: x + 2` with no other statement, so its Python
"Globals" frame has no bindings at all — the frame vanished from the
layout and the closure's arrow had nothing left to point to.

computeLiveState now also returns closureHomeEnvIds: the subset of
live environments that are some closure's/array's own environment (as
opposed to merely reachable via another live environment's tail
chain). Both collapsing paths skip an empty frame only when it's
outside that set.

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

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