feat(tvix/nix-compat/wire): have write_bytes accept AsRef<[u8]> payloads

This includes String, &str etc. An example testcase with &str is
provided.

Change-Id: I900186d6ceb52f52bd41ef4596524c1f5b52470b
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11376
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Reviewed-by: picnoir picnoir <picnoir@alternativebit.fr>

users/picnoir/tvix-daemon/src/main.rs

@@ -165,7 +165,7 @@ where
             // good idea.
             debug!("write version");
             // Plain str padded to 64 bits.
-            bytes::write_bytes(&mut conn, "2.3.17".as_bytes()).await?;
+            bytes::write_bytes(&mut conn, "2.3.17").await?;
             conn.flush().await?;
         }
         if protocol_minor >= 35 {