fix(matrix): reset _device_id_unverified at start of connect()

Per review feedback on #53997 from @teknium1: the flag was set True
on failed device_id resolution but never reset, so a same-adapter
reconnect that successfully resolves a real device_id would keep
skipping server-side key verification indefinitely.

Reset now happens at the top of connect(), before resolution runs,
so every connect() attempt starts clean. A repeat failure re-sets
the flag (unchanged behavior); a recovery correctly clears it.

Adds TestDeviceIdRecoveryOnReconnect to cover the transition.

plugins/platforms/matrix/adapter.py

@@ -1152,6 +1152,7 @@ class MatrixAdapter(BasePlatformAdapter):
 
     async def connect(self, *, is_reconnect: bool = False) -> bool:
         """Connect to the Matrix homeserver and start syncing."""
+        self._device_id_unverified = False
         if self._client is not None:
             try:
                 await self.disconnect()