test: use dynamic port allocation to avoid test conflicts

Use port=0 for dynamic port allocation in test framework components
to avoid "address already in use" errors from concurrent tests or
ports stuck in TIME_WAIT state from previous test runs.

Changes:
- socks5.py: Update conf.addr after bind() to reflect actual port
- p2p.py: Retrieve actual port after create_server() when port=0
- feature_proxy.py: Use port=0 for all SOCKS5 proxy servers
- feature_anchors.py: Use port=0 for onion proxy server

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