feat: track entity kills by player

src/main/java/com/prometheus/spigot/metrics/MetricsRegistry.java

@@ -51,6 +51,7 @@ public final class MetricsRegistry {
     private final ConcurrentHashMap<String, LongAdder> commandsBlocked = new ConcurrentHashMap<>();
     private final ConcurrentHashMap<LabelPair, LongAdder> commandsExecuted = new ConcurrentHashMap<>();
     private final ConcurrentHashMap<String, LongAdder> itemsCraftedByMaterial = new ConcurrentHashMap<>();
+    private final ConcurrentHashMap<LabelPair, LongAdder> entityKills = new ConcurrentHashMap<>();
 
     public MetricsRegistry(Server server, boolean enableJvm, boolean enableProcess) {
         this.server = server;
@@ -133,6 +134,12 @@ public final class MetricsRegistry {
         incrementLabeledCounter(itemsCraftedByMaterial, material.name());
     }
 
+    public void incrementEntityKill(EntityType entityType, String killer) {
+        String normalizedEntity = normalizeLabel(entityType.name());
+        String normalizedKiller = normalizeLabel(killer);
+        entityKills.computeIfAbsent(new LabelPair(normalizedEntity, normalizedKiller), key -> new LongAdder()).increment();
+    }
+
     public void refreshEntitySnapshots() {
         Map<String, Long> entityCounts = new HashMap<>();
         Map<String, Long> tileCounts = new HashMap<>();
@@ -184,6 +191,7 @@ public final class MetricsRegistry {
         appendLabeledCounterAdder(builder, "spigot_commands_blocked_total", "Blocked commands by name", "command", commandsBlocked);
         appendLabeledCounterAdder(builder, "spigot_commands_executed_total", "Commands executed by source", "command", "source", commandsExecuted);
         appendLabeledCounterAdder(builder, "spigot_items_crafted_total", "Items crafted by material", "material", itemsCraftedByMaterial);
+        appendLabeledCounterAdder(builder, "spigot_entities_killed_total", "Entities killed by player", "entity", "killer", entityKills);
 
         appendGauge(builder, "spigot_players_online", "Online player count", server.getOnlinePlayers().size());
         appendGauge(builder, "spigot_players_max", "Max player slots", server.getMaxPlayers());