Fix IMAP4WithTimeout compatibility with Python 3.14

Python 3.14 changed imaplib.IMAP4.file from a plain instance attribute
to a read-only property (see cpython commit introducing the change). The
open() override in IMAP4WithTimeout assigned to self.file directly, which
now raises:

    AttributeError: property 'file' of 'IMAP4WithTimeout' object has no setter

The fix mirrors what was already done for IMAP4_TLS in commit 64250b0:
remove the open() override entirely and instead pass the timeout through
to the parent __init__, which calls open() itself using self._file
internally. The _create_socket override is kept as-is so the stored
self._timeout fallback still applies for any call path that omits an
explicit timeout.

Fixes #638

Author: 736-c41-2c1-e464fc974

imapclient/imap4.py

@@ -10,16 +10,7 @@
 class IMAP4WithTimeout(imaplib.IMAP4):
     def __init__(self, address: str, port: int, timeout: Optional[float]) -> None:
         self._timeout = timeout
-        imaplib.IMAP4.__init__(self, address, port)
-
-    def open(
-        self, host: str = "", port: int = 143, timeout: Optional[float] = None
-    ) -> None:
-        # This is overridden to make it consistent across Python versions.
-        self.host = host
-        self.port = port
-        self.sock = self._create_socket(timeout)
-        self.file = self.sock.makefile("rb")
+        super().__init__(address, port, timeout=timeout)
 
     def _create_socket(self, timeout: Optional[float] = None) -> socket.socket:
         return socket.create_connection(