Merge bitcoin/bitcoin#34186: test: use dynamic port allocation in proxy tests

ce63d37ebe test: use dynamic port allocation to avoid test conflicts (woltx)

Pull request description:

  Use `port=0` for dynamic port allocation in test framework components to avoid intermittent "address already in use" errors when running tests concurrently or when ports are stuck in TIME_WAIT state. Example: https://github.com/bitcoin/bitcoin/pull/29415#discussion_r2634509304

  Changes:

    - Update `socks5.py` and `p2p.py` to support dynamic port allocation
    - Convert `feature_proxy.py` and `feature_anchors.py` to use `port=0`

ACKs for top commit:
  achow101:
    ACK ce63d37ebe
  vasild:
    ACK ce63d37ebe
  mzumsande:
    re-ACK ce63d37ebe

Tree-SHA512: 4efcedca3bde209fbd1bdc2a4ae04b7d53515587d86e421ce61064f78c675c71b45d9782b514c5e7cfc0e92842c947d49f7a3fddb03fe619fcdec9b565f0ecbd

test/functional/test_framework/p2p.py

@@ -787,13 +787,14 @@ class NetworkThread(threading.Thread):
                 cls.protos[(addr, port)] = None
             return response
 
-        if (addr, port) not in cls.listeners:
+        if port == 0 or (addr, port) not in cls.listeners:
             # When creating a listener on a given (addr, port) we only need to
             # do it once. If we want different behaviors for different
             # connections, we can accomplish this by providing different
             # `proto` functions
 
             listener = await cls.network_event_loop.create_server(peer_protocol, addr, port)
+            port = listener.sockets[0].getsockname()[1]
             logger.debug("Listening server on %s:%d should be started" % (addr, port))
             cls.listeners[(addr, port)] = listener
 

test/functional/test_framework/socks5.py

@@ -203,6 +203,9 @@ class Socks5Server():
         self.s = socket.socket(conf.af)
         self.s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
         self.s.bind(conf.addr)
+        # When port=0, the OS assigns an available port. Update conf.addr
+        # to reflect the actual bound address so callers can use it.
+        self.conf.addr = self.s.getsockname()
         self.s.listen(5)
         self.running = False
         self.thread = None