Refactor email handling for improved structure

Refactored `Email` and `SendingEmailEvent` to use `record` types, consolidating email-related data into the `Email` class. Updated `SendEmailCommand` to return a `Guid` and simplified mapping logic in `EmailMappingProfile`. Adjusted `SendEmailCommandHandler` to construct `SendingEmailEvent` manually.

Updated `SendingEmailConsumer`, `EmailsController`, and `EmailSender` to reflect the new structure. Removed the old `Email` implementation. Improved logging to reference the `Mail` property.

Revised tests to align with the new structure, ensuring immutability and better separation of concerns.

tests/DigitalData.MessagingService.Tests/Integration/EmailSenderTests.cs

@@ -77,6 +77,7 @@ public sealed class EmailSenderTests
     {
         var email = new Email
         {
+            Sender = new EmailAccountDto { Username = "test@example.com", Password = "password", SmtpServer = "smtp.example.com" },
             Recipients = ["hakanttek@gmail.com"],
             Subject = "EmailSender.Send Integration Test",
             Body = "<p>Sent via EmailSender static client.</p>",
@@ -93,6 +94,7 @@ public sealed class EmailSenderTests
     {
         var email = new Email
         {
+            Sender = new EmailAccountDto { Username = "test@example.com", Password = "password", SmtpServer = "smtp.example.com" },
             Recipients = ["hakanttek@gmail.com"],
             Subject = "Plain Text Test",
             Body = "This is a plain text email.",