Issue

We store attachments encoded in base64 in the database; the current library API does not allow sending pre-encoded attachments. Instead, we have to decode them and then provide them to the library to re-encode just before sending them.

Steps to Reproduce

1. Create an builder using EmailBuilder.startingBlank().
2. Add an attachment that is already encoded, for example in base64
3. Call EmailBuilder#build for create new email.
4. Call Mailer#send for send email.

Expected Behavior

The attachment will not be re-encoded, but will be sent in the current encoding.

Actual Behavior

The attachment will be re-encoded

Request

It is necessary to be able to indicate that the attachment is already encoded and specify the encoding. The library should use jakarta.mail.internet.PreencodedMimeBodyPart as a container for such attachments.