smol: Use Unblock instead of Async for stdin, stdout and stderr handles (#46141)

as per its documentation:

`Async` supports all networking types, as well as some OS-specific file
descriptors like timerfd and inotify.

However, do not use `Async` with types like File, Stdin, Stdout, or
Stderr because all operating systems have issues with them when put in
non-blocking mode.

Release Notes:

- N/A *or* Added/Fixed/Improved ...

crates/nc/src/nc.rs

@@ -16,15 +16,15 @@ pub fn main(_socket: &str) -> Result<()> {
 pub fn main(socket: &str) -> Result<()> {
     use futures::{AsyncReadExt as _, AsyncWriteExt as _, FutureExt as _, io::BufReader, select};
     use net::async_net::UnixStream;
-    use smol::{Async, io::AsyncBufReadExt};
+    use smol::{Unblock, io::AsyncBufReadExt};
 
     smol::block_on(async {
         let socket_stream = UnixStream::connect(socket).await?;
         let (socket_read, mut socket_write) = socket_stream.split();
         let mut socket_reader = BufReader::new(socket_read);
 
-        let mut stdout = Async::new(std::io::stdout())?;
-        let stdin = Async::new(std::io::stdin())?;
+        let mut stdout = Unblock::new(std::io::stdout());
+        let stdin = Unblock::new(std::io::stdin());
         let mut stdin_reader = BufReader::new(stdin);
 
         let mut socket_line = Vec::new();

crates/remote_server/src/unix.rs

@@ -32,7 +32,7 @@ use reqwest_client::ReqwestClient;
 use rpc::proto::{self, Envelope, REMOTE_SERVER_PROJECT_ID};
 use rpc::{AnyProtoClient, TypedEnvelope};
 use settings::{Settings, SettingsStore, watch_config_file};
-use smol::Async;
+
 use smol::channel::{Receiver, Sender};
 use smol::io::AsyncReadExt;
 use smol::{net::unix::UnixListener, stream::StreamExt as _};
@@ -627,19 +627,19 @@ pub(crate) fn execute_proxy(
     })?;
 
     let stdin_task = smol::spawn(async move {
-        let stdin = Async::new(std::io::stdin())?;
+        let stdin = smol::Unblock::new(std::io::stdin());
         let stream = smol::net::unix::UnixStream::connect(&server_paths.stdin_socket).await?;
         handle_io(stdin, stream, "stdin").await
     });
 
     let stdout_task: smol::Task<Result<()>> = smol::spawn(async move {
-        let stdout = Async::new(std::io::stdout())?;
+        let stdout = smol::Unblock::new(std::io::stdout());
         let stream = smol::net::unix::UnixStream::connect(&server_paths.stdout_socket).await?;
         handle_io(stream, stdout, "stdout").await
     });
 
     let stderr_task: smol::Task<Result<()>> = smol::spawn(async move {
-        let mut stderr = Async::new(std::io::stderr())?;
+        let mut stderr = smol::Unblock::new(std::io::stderr());
         let mut stream = smol::net::unix::UnixStream::connect(&server_paths.stderr_socket).await?;
         let mut stderr_buffer = vec![0; 2048];
         loop {