fix(net): stabilize socket handles and reactor paths

[andrewtdiz]

Summary

• register the ext-net socket handle probe so dynamic/static instanceof net.Socket and the net.Stream alias recognize native socket handles
• route ext-net socket connect and server listen futures through explicit current-thread Tokio runtimes instead of relying on an ambient reactor handle
• preserve net.Stream === net.Socket behavior while making new net.Stream() instanceof net.Socket match Node

Validation

• cargo fmt --all -- --check
• git diff --check
• ./scripts/check_file_size.sh
• cargo check -q -p perry-ext-net -p perry-codegen -p perry-runtime
• PATH=/root/.npm/_npx/bac97da9607b7ef2/node_modules/.bin:$PATH PERRY_NO_AUTO_OPTIMIZE=1 timeout 900 ./run_parity_tests.sh --suite node-suite --module net -> 13 pass / 0 fail / 0 compile fail (test-parity/reports/parity_report_20260605_061937.json)
• focused reruns: stream-alias, connection-state-limits, create-server-options, listen-port, socket-set-timeout all pass