Isolate live WebSocket smoke test from CI

[Ganador1]

Summary

• remove the import-time Binance WebSocket side effect from the test suite
• make the live-network smoke test explicitly opt-in with FENIX_RUN_NETWORK_TESTS=1
• retain a bounded 10-second connection timeout and validate the expected depth payload

Validation

• pytest -q tests/test_ws.py: skipped safely by default
• ruff check tests/test_ws.py: passed
• full local suite before this isolation fix: 1107 passed, 4 skipped
• post-merge security gates: Ruff, Bandit, Semgrep, pip-audit, npm audit, and secret scan passed