fix(ext/node): close accepted connections that sent no request on server.close()
A connection that was accepted but never sent a request was not treated as
idle, so server.close() left it open and its callback never ran. The socket
has no _httpMessageDetached, which is what closeIdleConnections used as its
idle test, so it fell through.
Track whether a request has actually begun on the wire, separately from the
connections-list entry pushed at accept time for headersTimeout, and treat a
connection with no request in progress as idle.
Node cannot reach this state: close() stops accepting, so such a connection
is still in the accept queue and gets reset. Deno accepts eagerly, so the
connection is already tracked and pins the server open. This follows the
behavior Node documents, and makes Node's own regression test for it pass -
test-http-server-close-idle-connections-pre-request.js, enabled here.
Closes #36513