Refactor damage source checking and restructure player management

The source of damage detection for PvP interactions has been updated to improve accuracy and flexibility. A 'Target' sub-class has been implemented in the PlayerManager class, removing the need for a separate DamageCheck class. The PlayerManager class was also moved to the 'data' package. Distribution of feedback messages has been simplified using the new DamageCheckResult class.

src/main/java/me/youhavetrouble/preventstabby/data/Target.java

@@ -0,0 +1,71 @@
+package me.youhavetrouble.preventstabby.data;
+
+import org.bukkit.entity.Entity;
+import org.bukkit.entity.Player;
+import org.bukkit.entity.Projectile;
+import org.bukkit.entity.Tameable;
+import org.jetbrains.annotations.NotNull;
+
+import javax.annotation.Nullable;
+import java.util.UUID;
+
+public class Target {
+
+    /**
+     * The unique identifier for a player.
+     */
+    public final UUID playerUuid;
+
+    /**
+     * Represents the entity classifier of a target.
+     * This indicates what type of entity player's id was assumed from
+     */
+    public final EntityClassifier classifier;
+
+    private Target(UUID uuid, EntityClassifier classifier) {
+        this.playerUuid = uuid;
+        this.classifier = classifier;
+    }
+
+    /**
+     * Get the UUID of the actual player, being owner of a pet, shooter of a projectile, etc.
+     *
+     * @param entity Base entity to get the player UUID from
+     * @return UUID of the actual player, null if not found
+     */
+    @Nullable
+    public static Target getTarget(@NotNull Entity entity) {
+        if (entity instanceof Player) return new Target(entity.getUniqueId(), EntityClassifier.PLAYER);
+
+        // Get shooter of projectile
+        if (entity instanceof Projectile projectile) {
+            if (projectile.getShooter() instanceof Player shooter) {
+                return new Target(shooter.getUniqueId(), EntityClassifier.PLAYER);
+            }
+        }
+
+        // Get player riding mount
+        if (!entity.getPassengers().isEmpty()) {
+            Entity passenger = entity.getPassengers().get(0);
+            if (passenger instanceof Player) {
+                return new Target(passenger.getUniqueId(), EntityClassifier.MOUNT);
+            }
+        }
+
+        // Get owner of tamed entity
+        if (entity instanceof Tameable tameable) {
+            if (tameable.getOwner() != null) {
+                return new Target(tameable.getOwner().getUniqueId(), EntityClassifier.PET);
+            }
+        }
+
+        return null;
+    }
+
+    public enum EntityClassifier {
+        PLAYER,
+        PET,
+        MOUNT,
+        OTHER
+    }
+}