Refactor FetchEmailsQuery and improve UID handling

Moved the `Folder` property from `FetchEmailsQuery` to the
`MailQuery` record to better encapsulate query parameters.
Updated `FetchEmailsQueryHandler` to use `MailQuery.Folder`
for improved modularity. Simplified UID limiting logic in
`LimilabsImapEmailService` by replacing `Take().ToList()`
with the more concise `[.. Take()]` syntax.

src/infrastructure/DigitalData.MessagingService.Infrastructure/Services/LimilabsImapEmailService.cs

@@ -44,7 +44,7 @@ public class LimilabsImapEmailService(
             // Most-recent first; honour maxCount
             uids.Reverse();
             if (maxCount > 0 && uids.Count > maxCount)
-                uids = uids.Take(maxCount).ToList();
+                uids = [.. uids.Take(maxCount)];
 
             var results = new List<ReceivedEmailContext>(uids.Count);