refactor: rename User to UserRegister

Renamed the User class to UserRegister to better reflect its purpose in registration-related operations.

Author: OmarElsheikh1

src/main/java/com/omarelsheikh/todo/models/User.java renamed to src/main/java/com/omarelsheikh/todo/models/UserRegister.java

@@ -1,6 +1,6 @@
 package com.omarelsheikh.todo.models;
 
-public class User {
+public class UserRegister {
 
     private String email;
     private String firstName;
@@ -9,7 +9,7 @@ public class User {
 
     // Constructor used to initialize all fields when creating a new User object
     // Useful when we want to set values directly at the time of object creation
-    public User(String email, String firstName, String lastName, String password) {
+    public UserRegister(String email, String firstName, String lastName, String password) {
         this.email = email;
         this.firstName = firstName;
         this.lastName = lastName;