Guard Folia creature cause expansion by region ownership

[baichuan335]

Summary

Fixes #2311.

On Folia, Cause.Builder can expand a projectile shooter that belongs to another Region. For creature shooters, that expansion reads mutable AI state through Creature#getTarget() (and for creepers Creeper#getTarget() / getIgniter()), which violates Folia ownership rules during vehicle damage handling.

This change keeps the projectile, shooter, and other cause objects in the cause chain, but skips only the mutable creature AI-state expansion when the creature is not owned by the current Region. Non-Folia behavior is unchanged, and locally owned Folia creatures retain the existing expansion behavior.

Verification

• ./gradlew.bat build -s --max-workers=1
  • Passed on the WorldGuard branch.
  • Includes unit tests, Checkstyle, header verification, and packaging.
• Official Folia runtime reproduction:
  • Folia 1.21.11-14, commit 529aabc
  • WorldEdit 7.4.3+7515-78babeb
  • WorldGuard 7.0.17 with this fix applied
  • Java 25.0.4.1
  • Four Region tick threads
  • Deterministic projectile/vehicle damage test
  • Result: projectile-owned-by-current=true
  • Result: shooter-owned-by-current=false
  • Result: VehicleDamageEvent returned; cancelled=true with global vehicle-destroy: deny
  • No Thread failed main thread check, CraftMob.getTarget() cross-Region exception, or other exception/error output

The same runtime behavior was also compared against the newer Folia 26.2 environment separately; that version changes projectile shooter ownership behavior, so it was not used as evidence for the original issue.