Items should normally only be inserted/extracted by either breaking the chamber, or using pressure chamber interfaces, both of which consume air.

But plenty mods allow insertion of items into the chamber without breaking it. Look at ways of preventing that.

• The items in the chamber are currently real item entities. We could have it so the chamber just renders the items, but they don't exist as entities.
• Any real items in the chamber would need to be converted to fake items when the multiblock is formed, and converted back when the multiblock is broken.
• The interface would no longer create or destroy item entities, but just update the pressure chamber's internal list of chambered items.
• The pressure chamber would need a TESR to render those chambered items.

This is merged to master now.