Assorted ZAS fixes

[NataKilar]

Description of changes

An assortment of ZAS fixes, mostly related to the creation of unsimulated edges between zones and space.

• Creating a hole in the floor into space will now create an unsimulated edge as expected. This is done by checking if the zone_membership_candidate variable has changed to FALSE during a turf change. Every other case should be covered by the typical checks for exterior atmosphere participation.
• Changed the default open_turf for flooring and natural flooring to airless variants of open space. This fixes a bug where space tiles weren't being removed from Z-stacks when the bottom most space tile was replaced by plating. I haven't tested how this affects issue #3999 yet.
• Doors and other atoms that need to update ZAS connections will now update their loc's neighbors if the atom is located on top of an exterior turf. This fixes a bug where unsimulated edges weren't being updated or created as expected.
• Fixes a longstanding issue where connections for ZAS edges in the up and down direction weren't being added to turfs' connection managers

Why and what will this PR improve

Fixes a variety of ZAS issues stemming from the simulated/unsimulated turf merger. There is still an issue with gas conservation when merging two zones between z-levels, which I still need to resolve.

Authorship

Myself. Thanks to Penny for the multi-Z get_dir code.

Changelog

:cl: bugfix: Fixed space tiles not creating vacuums in certain conditions /:cl: