scp2: use monad for/yield syntax

scala_project_2025/bank_system/src/main/scala/Bank.scala

@@ -73,23 +73,15 @@ class Bank(val allowedAttempts: Integer = 3) {
   private def processSingleTransaction(t: Transaction): Thread =
     new Thread(() => {
       accountsRegistry.synchronized {
-        val fromOpt = getAccount(t.from)
-        val toOpt = getAccount(t.to)
-
-        (fromOpt, toOpt) match {
-          case (Some(from), Some(to)) =>
-            from.withdraw(t.amount) match {
-              case Right(updatedFrom) =>
-                to.deposit(t.amount) match {
-                  case Right(updatedTo) =>
-                    accountsRegistry(t.from) = updatedFrom
-                    accountsRegistry(t.to) = updatedTo
-                    t.succeed()
-                  case Left(_) => t.fail()
-                }
-              case Left(_) => t.fail()
-            }
-          case _ => t.fail()
+        for {
+          from <- getAccount(t.from)
+          to <- getAccount(t.to)
+          updatedFrom <- from.withdraw(t.amount).toOption
+          updatedTo <- to.deposit(t.amount).toOption
+        } yield {
+          accountsRegistry(t.from) = updatedFrom
+          accountsRegistry(t.to) = updatedTo
+          t.succeed()
         }
       }
     })