Stop receiving when a UDPTransport handle is closed directly

UDPTransport keeps a reference to itself while receiving, which was
only dropped by _stop_reading(). loop.close() closes leftover handles
with _close(), so a UDP transport still open at that point was never
freed. Stop reading in _close(), as UVStream does.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: graingert

uvloop/handles/udp.pxd

@@ -13,6 +13,8 @@ cdef class UDPTransport(UVBaseTransport):
     cdef open(self, int family, int sockfd)
     cdef _set_broadcast(self, bint on)
 
+    cdef _close(self)
+
     cdef inline __receiving_started(self)
     cdef inline __receiving_stopped(self)
 

uvloop/handles/udp.pyx

@@ -171,6 +171,14 @@ cdef class UDPTransport(UVBaseTransport):
         else:
             self.__receiving_stopped()
 
+    cdef _close(self):
+        try:
+            # Drop the reference held while receiving, even when the
+            # handle is closed directly (e.g. by loop.close()).
+            self._stop_reading()
+        finally:
+            UVSocketHandle._close(<UVHandle>self)
+
     cdef inline __receiving_started(self):
         if self.__receiving:
             return