fix: ensure child effects are removed from parent branches

[trueadm]

This should prevent the effects array of a branch effect from growing indefinitely – causing memory leaks.

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[Rich-Harris]

This is presumably quite costly if you're removing large numbers of items from an each block (for each of . Do we definitely want to do this, or should we go straight to a linked list implementation?

At the very least we should probably update pause_effects so that it works backwards, since splicing from the end is much cheaper than splicing from the beginning

[trueadm]

@Rich-Harris I looked at this is a temp fix until I've implanted linked lists. Ideally we'd use the controlled input to just wipe all children in one go.