Add Luxury Market for MVP Card Vendors

Imported from legacy Flarum.
Original author: Aqua (Flarum #629)

Could we have a custom market for highly-priced items (specifically MVP Cards) that could hold up to ~30b value of items (if there’s such that exists).

Basically, there would be an NPC to trade your Zeny for Diamonds (similar to 17C Diamonds) that has a value of 1m each, and 970k each when you re-convert it back to Zeny, to simulate the 3% vend tax.

Vendors would put up prices in this market as if 1 Zeny (1 Diamond) = 1m Zeny, so if I want to put up an item for 5b, it would mark as 5,000 Zeny, but it won’t accept Zeny, only the special Diamonds from the Luxury Market.