Add WS bridge over DAP TCP server

[rentziass]

This adds a bridge converting messages to/from TCP <-> WS so that we can connect to the DAP server through wss:// directly and using GitHub credentials out of the box with Dev Tunnels.

https://github.com/github/c2c-actions/issues/9831

[Copilot]

Pull request overview

This PR introduces a WebSocket-to-TCP bridge in the DAP subsystem so remote debugging can connect via ws:///wss:// to the runner’s DAP server (e.g., through Dev Tunnels using GitHub auth), while the internal DAP server continues to speak DAP-over-TCP.

Changes:

• Add WebSocketDapBridge to translate WebSocket text frames ↔ DAP TCP (Content-Length framed) messages.
• Update DapDebugger startup/shutdown to expose the tunnel port via the WebSocket bridge and move the internal DAP listener to an ephemeral local port.
• Add L0 coverage for the bridge and for DapDebugger WebSocket connectivity (including “pre-upgraded” WebSocket streams).

Show a summary per file

File	Description
src/Runner.Worker/Dap/WebSocketDapBridge.cs	New bridge implementation handling upgrade detection, handshake, and bidirectional message pumping.
src/Runner.Worker/Dap/DapDebugger.cs	Starts/stops the bridge and uses an internal ephemeral TCP port for the actual DAP server when the bridge is enabled.
src/Test/L0/Worker/WebSocketDapBridgeL0.cs	New L0 tests validating forwarding, rejection paths, message size limits, and disposal behavior.
src/Test/L0/Worker/DapDebuggerL0.cs	Extends L0 tests to validate DapDebugger can accept DAP initialize via WebSocket and pre-upgraded WebSocket streams.

Copilot's findings

• Files reviewed: 4/4 changed files
• Comments generated: 7

[TingluoHuang]

do you want to wrap this as IRunnerService, so you don't have to pass in a tracer.

[TingluoHuang]

do you want to explicit shutdown the WebSocketDapBridge from the caller?
ex: we can just make a method call public async Task Shutdown()