Change ws engine of server to bun

[Exeloo]

Scope

• TCPServer and UDPServer move from ws + node:https to Bun.serve()
• The TLS/non-TLS branches collapse into one call with optional tls; the duplicated
  startWebSocketServer helper is removed
• Per-connection state moves to ws.data; server.requestIP() replaces
  request.socket.remoteAddress
• Remove ws and @types/ws; add @types/bun
• tsconfig.server.json gets types: ["bun"] and skipLibCheck: true (the latter is a
  real loosening — node-datachannel's .d.ts conflicts with the DOM lib)
• __clear() teardown is implemented so the servers actually release their ports
• Tests move from vi.mock("ws") to vi.stubGlobal("Bun", …) — Bun is a global, so
  vi.mock cannot intercept it

Breaking change

@nanoforge-dev/network/server now requires Bun and no longer runs on Node, as accepted
in this issue. The client entry point is unaffected. Note @nanoforge-dev/loader-server
is currently built with bun build --target node, so it must move before nf start
works with this.

Scope boundary

Bun.serve() speeds up signalling only. The UDP data channel is libdatachannel's own
C++ sockets and never touches Bun's networking — benchmarked at 20k msgs × 200 B, three
runs each: Bun 52.8/49.8/51.5k msg/s vs Node 46.8/48.3/49.9k msg/s. The ranges overlap;
there is no meaningful difference on the media path.