[andrewtdiz]

Summary

• Adds a child-side process IPC runtime surface initialized from NODE_CHANNEL_FD.
• Exposes live process.send, process.disconnect, process.connected, and process.channel.ref/unref through direct process reads and native module namespace objects.
• Drains child IPC messages through the process EventEmitter pump and keeps the loop alive only after message/disconnect listeners or explicit channel.ref().
• Adds parity coverage for no-IPC reads and forked child JSON message round-trips.

Closes #2529.

Notes

• This implements newline-delimited JSON child IPC framing. Advanced serialization and handle passing are left out of this cut.
• NODE_CHANNEL_FD and NODE_CHANNEL_SERIALIZATION_MODE are removed before process.env materialization to match Node bootstrap behavior.

Validation

• cargo fmt --all -- --check
• git diff --check
• ./scripts/check_file_size.sh
• cargo check -p perry-runtime -p perry-hir -p perry-codegen -p perry-api-manifest
• ./run_parity_tests.sh --suite node-suite --module process --filter child-channel
• ./run_parity_tests.sh --suite node-suite --module process --filter ipc
• ./run_parity_tests.sh --suite node-suite --module child_process --filter fork-send-callback-closed (local Node cannot run this .ts fixture; skip-only threshold failure)
• ./run_parity_tests.sh --suite node-suite --module child_process --filter fork-child-shape (local Node cannot run this .ts fixture; skip-only threshold failure)