Apply BentoBox admin deaths commands to island deaths

[tastybento]

Why

Discord report: an admin ran /bsbadmin deaths remove <player> 3 ("decreasing the total to 0 deaths"), but /is level still showed (3 deaths). Since 2.29.0 (ff59b02) Level keeps deaths per island and reads BentoBox's per-world counter only once, when it migrates an island. After that, the admin deaths commands had no effect on levels, and Level had no command of its own to change them.

Instead of adding a duplicate Level command, Level now reacts to the BentoBox command.

What

• New AdminDeathsListener handles PlayerDeathsChangedEvent (Fire PlayerDeathsChangedEvent from admin deaths commands BentoBox#3093) and applies it to every island the player is a member of in that game mode. Islands where they're only trusted or coop are skipped.
• New LevelsManager methods:
  • addDeaths: adds to the player's count, capped at deaths.max.
  • removeDeaths: takes from the player's count first, then any remainder from the island's anonymous deaths, never below 0.
  • setDeaths (also used for reset): sets the player's count and clears anonymous deaths. The migrated seed lives in the anonymous count, so without this a reset wouldn't fix the reported case. On team islands this also clears deaths left behind by former members; other current members' counts aren't touched.
• The listener is only registered if the running BentoBox has the event. On older BentoBox, Level logs a note and otherwise works as before.
• Comments in config.yml and ConfigSettings now describe this behaviour.
• The BentoBox dependency moves from 3.15.1-SNAPSHOT to 3.23.1-SNAPSHOT.

Merge order

1. Fire PlayerDeathsChangedEvent from admin deaths commands BentoBox#3093, then a 3.23.1-SNAPSHOT containing it has to be published.
2. Build with JDK 25 in CI #460, which fixes the ItemsAdder dependency repo (it currently breaks CI on develop).
3. This PR. CI here will fail until 1 and 2 are done.

Tested locally against a locally published core build: all 267 tests pass, including new LevelsManagerTest cases and AdminDeathsListenerTest.

Release note

Admins need to update both BentoBox and Level for /<admin> deaths to affect island levels.

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