Folia support: migrate Bukkit scheduler usage to SchedulerUtils

[GenOpenDiesel]

Why

plugin.yml already declares folia-supported: true, but the plugin still scheduled work through the global BukkitScheduler / BukkitRunnable, which throws on Folia. There was even a leftover //TODO folia fix in Usable. On Folia reload() would also blow up because EquipmentChangeListenerBase started a runTaskTimer on the global scheduler.

What

Migrated every scheduler call to ItemEdit's Folia-aware SchedulerUtils, scoping each task to the player it acts on so it runs on that entity's region thread.

One-shot delayed tasks (runTaskLater / BukkitRunnable):

• customflags/Usable (removes the //TODO folia fix)
• customflags/EquipmentFlag
• customflags/RenamableOld
• command/itemtag/WearPermission
• command/itemtag/EffectsResurrectListener
• command/itemtag/Effects (respawn + milk-bucket consume)
• actions/DelayedAction
• activity/action/DelayedActionType

Equipment change listener:

• SlotCheck no longer extends BukkitRunnable — it implements Runnable and exposes schedule() backed by SchedulerUtils.runLater(plugin, player, 1L, this). All new SlotCheck(...).runTaskLater(...) call sites (Base + EquipmentChangeListener + UpTo1_13 + UpTo1_8) now call .schedule().
• The periodic equipment poll keeps the existing BukkitRunnable timer off Folia (unchanged behaviour, including max_checked_players_per_tick spreading). On Folia it self-reschedules through SchedulerUtils and fans each player's check out to that player's own region thread.
• equips / clickDrop are backed by thread-safe collections on Folia (mirrors the existing ActionHandler ConcurrentHashMap handling), since they are now touched from per-player region threads.

Notes

• No new dependency: SchedulerUtils ships with ItemEdit (already a compile dependency).
• Non-Folia behaviour is intentionally left identical — only the Folia branch is new.
• Builds cleanly with mvn package against spigot-api 1.21.x. I don't have a Folia server to runtime-test the equipment-poll path, so that part would benefit from a check on a live Folia instance.

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