Add mailboxes to Minecraft

Any Chest or Barrel can become a "Mailbox" when you place it down and apply a Nametag to it. Picking it up again keeps the Nametag of course, and they are not stackable in inventory. The Nametag can contain any combination of legal characters, and it will always appear as a label and be visible to anyone who opens the Mailbox to look inside.

A mailbox works like this: You put something in the Mailbox, and after three Minecraft day cycles (72,000 ticks), everything you put in the mailbox is now accessible to every other Mailbox that has the same Nametag name.

Caveat: Any time you open a Mailbox and put something new in it, the counter resets back to zero. So make sure you are 'mailing' everything you want to ship off to wherever or whomever.

Of course, going to sleep through the night could fast forward the timer to the next sunrise. Maybe this can be a gamerule that some players want to turn off or leave on.

And as you would expect, if you change the Nametag on a Mailbox, it no longer has access to that Nametag's items.

There should also be a procedure worked out for the use case of someone changing a Mailbox's Nametag while another player is accessing its contents.

There might be a need to indicate to a player how many total instances of a Mailbox+Nametag are known to exist in the world, so they can be sure they got the name right.