TF-56 Send email with attachment

model/lib/extensions/attachment_extension.dart

@@ -0,0 +1,12 @@
+
+import 'package:jmap_dart_client/jmap/mail/email/email_body_part.dart';
+import 'package:model/model.dart';
+
+extension AttachmentExtension on Attachment {
+  EmailBodyPart toEmailBodyPart(String disposition) => EmailBodyPart(
+    blobId: blobId,
+    size: size,
+    name: name,
+    type: type,
+    disposition: disposition);
+}

model/lib/extensions/email_body_part_extension.dart

@@ -0,0 +1,13 @@
+import 'package:jmap_dart_client/jmap/mail/email/email_body_part.dart';
+import 'package:model/model.dart';
+
+extension EmailBodyPartExtension on EmailBodyPart {
+  Attachment toAttachment() => Attachment(
+    partId: partId,
+    blobId: blobId,
+    size: size,
+    name: name,
+    type: type,
+    cid: cid,
+    disposition: disposition);
+}