refactor: update meterRegistry usage to Option type and improve formatting

modules/account/src/main/scala/de/nowchess/account/service/AccountService.scala

@@ -61,7 +61,7 @@ class AccountService:
   def login(req: LoginRequest): Either[AccountError, String] =
     val result = authenticateUser(req)
     result match
-      case Right(_)    => meterRegistry.counter("nowchess.auth.logins", "result", "success").increment()
+      case Right(_) => meterRegistry.counter("nowchess.auth.logins", "result", "success").increment()
       case Left(error) =>
         meterRegistry.counter("nowchess.auth.logins", "result", "failure").increment()
         meterRegistry.counter("nowchess.auth.login.failures", "reason", loginFailureReason(error)).increment()

modules/account/src/main/scala/de/nowchess/account/service/ChallengeService.scala

@@ -118,7 +118,11 @@ class ChallengeService:
     result.foreach(_ => meterRegistry.counter("nowchess.challenges.declined").increment())
     result
 
-  private def declineChallenge(challengeId: UUID, userId: UUID, req: DeclineRequest): Either[ChallengeError, Challenge] =
+  private def declineChallenge(
+      challengeId: UUID,
+      userId: UUID,
+      req: DeclineRequest,
+  ): Either[ChallengeError, Challenge] =
     for
       challenge <- challengeRepository.findById(challengeId).toRight(ChallengeError.ChallengeNotFound)
       _         <- Either.cond(challenge.status == ChallengeStatus.Created, (), ChallengeError.ChallengeNotActive)

modules/official-bots/src/main/scala/de/nowchess/bot/logic/AlphaBetaSearch.scala

@@ -15,7 +15,7 @@ final class AlphaBetaSearch(
     tt: TranspositionTable = TranspositionTable(),
     weights: Evaluation,
     numThreads: Int = Runtime.getRuntime.availableProcessors,
-    meterRegistry: MeterRegistry = null,
+    meterRegistry: Option[MeterRegistry] = None,
 ):
 
   private val INF                  = Int.MaxValue / 2
@@ -108,9 +108,10 @@ final class AlphaBetaSearch(
     result
 
   private def recordSearchMetrics(depthReached: Int): Unit =
-    if meterRegistry != null then
-      meterRegistry.summary("nowchess.bot.search.nodes").record(nodeCount.get().toDouble)
-      meterRegistry.summary("nowchess.bot.search.depth").record(depthReached.toDouble)
+    meterRegistry.foreach { mr =>
+      mr.summary("nowchess.bot.search.nodes").record(nodeCount.get().toDouble)
+      mr.summary("nowchess.bot.search.depth").record(depthReached.toDouble)
+    }
 
   private def isOutOfTime: Boolean =
     System.currentTimeMillis - timeStartMs.get >= timeLimitMs.get

modules/official-bots/src/main/scala/de/nowchess/bot/service/OfficialBotService.scala

@@ -19,11 +19,11 @@ import java.util.function.Consumer
 class OfficialBotService:
 
   // scalafix:off DisableSyntax.var
-  @Inject var redis: RedisDataSource         = uninitialized
-  @Inject var redisConfig: RedisConfig       = uninitialized
-  @Inject var objectMapper: ObjectMapper     = uninitialized
-  @Inject var botController: BotController   = uninitialized
-  @Inject var meterRegistry: MeterRegistry   = uninitialized
+  @Inject var redis: RedisDataSource       = uninitialized
+  @Inject var redisConfig: RedisConfig     = uninitialized
+  @Inject var objectMapper: ObjectMapper   = uninitialized
+  @Inject var botController: BotController = uninitialized
+  @Inject var meterRegistry: MeterRegistry = uninitialized
   // scalafix:on DisableSyntax.var
 
   private val terminalStatuses =