perf: optimize spawn cleanup removing redundant iteration (opentibiab…

…r#2913)

This improves efficiency by avoiding an intermediate list for removal,
saving time and memory. The map is traversed only once, with iterators
updated after each removal, making the process more efficient.
Additionally, it eliminates redundant lookups by directly modifying the
map during iteration.

src/creatures/monsters/spawns/spawn_monster.cpp

@@ -282,16 +282,17 @@ void SpawnMonster::scheduleSpawn(uint32_t spawnMonsterId, spawnBlock_t &sb, cons
 }
 
 void SpawnMonster::cleanup() {
-	std::vector<uint32_t> removeList;
-	for (const auto &[spawnMonsterId, monster] : spawnedMonsterMap) {
-		if (monster == nullptr || monster->isRemoved()) {
-			removeList.push_back(spawnMonsterId);
+	std::erase_if(spawnedMonsterMap, [this](const auto &entry) {
+		const auto &monster = entry.second;
+		if (!monster || monster->isRemoved()) {
+			auto spawnIt = spawnMonsterMap.find(entry.first);
+			if (spawnIt != spawnMonsterMap.end()) {
+				spawnIt->second.lastSpawn = OTSYS_TIME();
+			}
+			return true;
 		}
-	}
-	for (const auto &spawnMonsterId : removeList) {
-		spawnMonsterMap[spawnMonsterId].lastSpawn = OTSYS_TIME();
-		spawnedMonsterMap.erase(spawnMonsterId);
-	}
+		return false;
+	});
 }
 
 bool SpawnMonster::addMonster(const std::string &name, const Position &pos, Direction dir, uint32_t scheduleInterval, uint32_t weight /*= 1*/) {