refactor(core): encapsulate user and refresh token creation with factory methods

src/FiscalOS.Core/Identity/User.cs

@@ -6,4 +6,22 @@ public sealed class User : Entity
   public string HashedPassword { get; init; } = string.Empty;
 
   public ICollection<RefreshToken> RefreshTokens { get; init; } = [];
+
+  private User()
+  {
+  }
+
+  public static User New()
+  {
+    return new();
+  }
+
+  public static User From(string username, string hashedPassword)
+  {
+    return new()
+    {
+      Username = username,
+      HashedPassword = hashedPassword,
+    };
+  }
 }