fix(types): P3 — annotate transport in all template protocol servers; 0 errors in templates/

- asyncio.Protocol (TCP): _transport: asyncio.Transport | None = None + cast() in
  connection_made; assert guards in every method that directly accesses the field.
  Files: pop3, smtp, mqtt, postgres, mssql, mongodb, imap, ldap, redis, mysql, sip, vnc.
- asyncio.DatagramProtocol (UDP): _transport: asyncio.DatagramTransport | None = None.
  Files: snmp, tftp, SIPUDPProtocol.
- RDP: assert new_transport is not None after start_tls() to narrow Transport | None.
- FTP (Twisted): assert self.transport is not None + targeted type: ignore for imprecise
  Twisted stubs (misc/override/arg-type/attr-defined), IReactorTCP cast for listenTCP.
- conpot: proc.stdout is None guard before iteration.
- Bonus fixes surfaced by annotation:
  - smtp: get_payload(decode=True) bytes narrowing (arg-type on sha256)
  - postgres: rename shadowed `msg` param to `err_msg` in _handle_startup
  - mongodb: base64.binascii.Error → import binascii; binascii.Error
  - imap: result: list[int] = [] (var-annotated)

decnet/templates/ftp/server.py

@@ -7,9 +7,12 @@ forwards events as JSON to LOG_TARGET if set.
 
 import os
 from pathlib import Path
+from typing import cast
 
 from twisted.internet import defer, reactor
+from twisted.internet.interfaces import IReactorTCP
 from twisted.protocols.ftp import FTP, FTPFactory, FTPAnonymousShell
+from twisted.python.failure import Failure
 from twisted.python.filepath import FilePath
 from twisted.python import log as twisted_log
 
@@ -95,7 +98,8 @@ _BAIT_PATH = _setup_bait_fs()
 
 class ServerFTP(FTP):
     def connectionMade(self):
-        peer = self.transport.getPeer()
+        assert self.transport is not None
+        peer = self.transport.getPeer()  # type: ignore[misc]
         _log("connection", src_ip=peer.host, src_port=peer.port)
         super().connectionMade()
 
@@ -120,15 +124,16 @@ class ServerFTP(FTP):
             return defer.succeed((530, "Login incorrect."))
         self.state = self.AUTHED
         self._user = getattr(self, "_server_user", "anonymous")
-        self.shell = FTPAnonymousShell(FilePath(_BAIT_PATH))
+        self.shell = FTPAnonymousShell(FilePath(_BAIT_PATH))  # type: ignore[assignment]
         return defer.succeed((230, "Login successful."))
 
     def ftp_RETR(self, path):
         _log("download_attempt", path=path)
         return super().ftp_RETR(path)
 
-    def connectionLost(self, reason):
-        peer = self.transport.getPeer()
+    def connectionLost(self, reason: Failure) -> None:  # type: ignore[override]
+        assert self.transport is not None
+        peer = self.transport.getPeer()  # type: ignore[misc]
         _log("disconnect", src_ip=peer.host, src_port=peer.port)
         super().connectionLost(reason)
 
@@ -140,5 +145,5 @@ class ServerFTPFactory(FTPFactory):
 if __name__ == "__main__":
     twisted_log.startLoggingWithObserver(lambda e: None, setStdout=False)
     _log("startup", msg=f"FTP server starting as {NODE_NAME} on port {PORT}")
-    reactor.listenTCP(PORT, ServerFTPFactory())
-    reactor.run()
+    cast(IReactorTCP, reactor).listenTCP(PORT, ServerFTPFactory())  # type: ignore[arg-type]
+    reactor.run()  # type: ignore[attr-defined]