DoxCore

Added (API for other mods; nothing changes on its own)

- DoxPlayerStorage: a mod that keeps items outside the vanilla inventory (e.g. DoxBackpack's grid) can

  register as the place to put items given back to a player. give() falls back to the vanilla

  inventory, then drops at the feet; offer() inserts what fits and drops nothing.

- DoxStackClick: rules for putting one item onto another in a slot and taking it back out (e.g. loading

  rounds into a magazine), so non-vanilla screens can use them. Handlers can ask for a repeat interval

  while the button is held.

- DoxReadyItems: lets a storage mod expose the "ready" slots a player can reach instantly (pockets,

  chest rig) so reload logic can use magazines kept there.

The version number is raised because these are new classes: mixing this jar with an old 1.0.1 jar

would hide them. 1.21.1 (2.0.0) is unchanged.