Implements the Retrace spell and related usable items

[Nireya]

I affirm:

• that I agree to Project Topaz's Limited Contributor License Agreement, as written on this date
• that I've tested my code since the last commit in the PR, and will test after any later commits

Implements the retrace spell into the game, along with related usable items:

• Scroll of Instant Retrace
• Cobra staff
• Fourth staff
• Ram staff

The staves have separate teleport IDs from Retrace because you can use their teleports after joining a different allied nation.

Retrace was changed from an 8 second cast to a 5 second cast recently according to wiki so I adjusted that.

[zach2good]

All seems fine to me, thanks for acting on the others' feedback so promptly 👍

Today I learned about upack(), neat!