Bun parity: complete the WebSocket client echo matrix

Parent: #66 Predecessor: #392

Corpus position 4206/4708: js/web/websocket/websocket-client.test.ts.

The first url case currently remains pending because the spawned Node echo server cannot deliver its IPC URL through the corpus harness. The full file additionally exercises ready-state transitions, binaryType validation/conversion, text and binary sends, ping/pong payloads, clean close codes/reasons, and abrupt termination.

Implement the server as a real in-memory ws echo topology, preserve asynchronous IPC startup and child cleanup, and fix shared global/ws client semantics rather than classifying the file unsupported. Errors and state transitions must retain actionable context. Add a permanent exact-file regression and report the full upstream count.

Completed and pushed in f1805d6 (fix(websocket): complete client echo semantics).

The unchanged position-4206 upstream file is 29/29 with 0 failed, todo, unsupported, or allowed-empty cases. Home now preserves the complete client echo matrix: asynchronous echo-server IPC startup/cleanup, OPEN/CLOSING/CLOSED transitions, binaryType validation and Blob/ArrayBuffer/nodebuffer conversion, text/binary traffic, client/server ping-pong directionality, clean close codes/reasons, and abrupt termination.

A permanent exact-file regression guards all 29 cases. Successor: #394.