User module | Register Feature

# User Registration Process

## User Story

As a user, I am required to utilize a valid email and password to access the application. In the event that either the email or password provided is incorrect, the application is expected to display an error message indicating the invalidity of the login credentials. Specifically, in the case of an incorrect email, the error message should read "Invalid email address." Furthermore, if the email is valid but the password is incorrect, the error message should state "Invalid password."

## Task

1. Implement Data Access Object (DAO) Layer.
2. Implement Service Layer.
3. Create JUnit Test Cases.
4. Ensure that the test cases are passing.
5. Write clear and concise comments in the code to explain complex logic.

## DAO

- `createUser()`: Creates a new user in the database.

## Service

- `registerUser()`: Registers a new user using the Service Layer.

## JUnit Tests

- `testValidRegisterUser()`: Tests the registration of a valid user.
- `testInvalidRegisterUser()`: Tests the handling of invalid registration.

## Estimation

5.5 hours