feat: add training ground gamemode

[Muparadzi]

Training Ground

TODO

• [x] migration

A rework of Native Duel, without the weird teleport mechanics.

Duel cards have been redesigned to show MMR, W/L and other statistics. The cards/stats are synced with the database and persist over sessions.

Following a duel, the winning characters' health is restored to full. They can refresh their equipment on the pause menu (if a shield breaks, or they wish to load new equipment)

Rating has been moved into statistics to enable MMR tracking for different gamemodes.

A leaderboard option has been added to filter by duel rating

[Yeldur]

Will try to take a look at this over the weekend