This matches <https://redirect.github.com/helix-editor/helix/pull/4852>
for the DAP transport: when there is a failure to receive a message from
the debugger we should drain all pending requests and respond to them
with the StreamClosed error.
This improves the behavior when a debugger fails to initialize, for
example starting debugpy without debugpy installed. Previously the UI
would freeze until the request timed out. Now it instantly prints a
statusline error saying that the debugger failed to start up.
26db54155e