Other players on transports (boats, zeppelins, trams) were not properly
tracked because handleOtherPlayerMovement() did not read transport data
from MSG_MOVE_* packets. This caused entities to slide off transports
between movement updates since no transport attachment was established.
Now reads the transport GUID and local offset from the packet using
expansion-aware wire flags (0x200 for WotLK/TBC, 0x02000000 for
Classic/Turtle), registers a transport attachment so the entity follows
the transport smoothly via updateAttachedTransportChildren(), and clears
the attachment when the player disembarks.