Match get_mailbox annotations to what callers actually pass

get_mailbox declared port and security as always-present types, but
MailAccount.imap_port is nullable and imap_security is stored as a plain
integer, so type checking flagged every call site as passing the wrong
type.

Widen the annotations to port: int | None and security: int, matching the
model fields; IntegerChoices members still compare equal to plain ints, so
the existing branching in get_mailbox is unaffected.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/paperless_mail/mail.py

@@ -533,8 +533,8 @@ class PinnedMailBoxStartTls(PinnedClientMixin, MailBoxStartTls):
 
 def get_mailbox(
     server: str,
-    port: int,
-    security: MailAccount.ImapSecurity,
+    port: int | None,
+    security: int,
 ) -> MailBox:
     """
     Returns the correct MailBox instance for the given configuration.