Named pipes do not actually support `shutdown`, and this hack to fake it
was unsound. Return `UV_ENOTSOCK` from `uv_shutdown` immediately for
`UV_NAMED_PIPE` handles, matching the behavior on unix where `shutdown`
on a pipe fd fails with `ENOTSOCK` (as oppposed to a unix domain socket
which is also a `uv_pipe_t`, but does supposed `shutdown`).
Fixes tests to work correctly whether or not shutdown works.
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
064617e40a