Introduced `FetchEmailUidsQuery` to retrieve UIDs of matching
emails from an IMAP mailbox. Added the `FetchEmailUidsQuery`
record with properties for email account (`GetSenderQuery`)
and mail filtering (`MailSearchFilter`).
Implemented `FetchEmailUidsQueryHandler` to handle the query.
The handler validates the email account, ensures IMAP
configuration, and uses `IImapEmailService.FetchEmailUidsAsync`
to fetch UIDs. Added necessary `using` directives for
dependencies.
TekH
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