Net: honor listen=0 for embedded Tor

[cursor]

PR intention

Fix a regression where -listen=0 -torsetup=1 still bound a dedicated local listener for embedded Tor hidden-service forwarding. This made the node accept inbound onion traffic even though parameter interaction had disabled listening/listenonion.

Code changes brief

• Gate the embedded Tor dedicated onion listener on the effective -listen setting, while preserving explicit -listenonion=1 behavior.
• Add a proxy_test.py regression check that starts -listen=0 -torsetup=1 and verifies no extra loopback onion listener is bound.

Validation:

• python3 -m py_compile qa/rpc-tests/proxy_test.py
• Regex sanity check for the new log assertion
• Full functional test not run: no build artifacts or depends toolchain were present in the workspace.