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

src/main/java/dev/banking/model/BankAccount.java

@@ -5,6 +5,11 @@ public class BankAccount {
     private final int accountId;
     private long balance;
 
+    /*
+     * Students may introduce additional fields
+     * if required by their synchronization strategy.
+     */
+
     public BankAccount(int accountId, long initialBalance) {
         this.accountId = accountId;
         this.balance = initialBalance;