feat: implement TransactionProcessor with type-based dispatch for all transaction operations

src/main/java/dev/banking/service/BankingSystem.java

@@ -6,6 +6,18 @@ import dev.banking.processor.TransactionProcessor;
 import java.util.List;
 import java.util.concurrent.ExecutorService;
 
+/**
+ * Dispatches a list of transactions to a shared ExecutorService
+ * for concurrent (asynchronous) processing.
+ *
+ * Each transaction is submitted as an independent task and may
+ * be executed in parallel depending on thread availability.
+ *
+ * No ordering guarantees are provided between transactions.
+ *
+ * Lifecycle management of the ExecutorService (creation,
+ * shutdown, termination) is handled outside this class.
+ */
 public class BankingSystem {
 
     private final ExecutorService executor;