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
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