Port fetch (with fixes) (#660)

* Port fetch to engine-q

* Fix check for path as a string

* Add a timeout flag and fix some span issues

* Add a temporary fetch command that returns byte streams. Got rid of async stuff as we're using the blocking feature of tokio

* More tweaks for the bytestream

* Rewrite fetch using ByteStreams

* buffer read on bytes directly

Co-authored-by: Stefan Stanciulescu <contact@stefanstanciulescu.com>

crates/nu-command/src/default_context.rs

@@ -297,6 +297,9 @@ pub fn create_default_context() -> EngineState {
         #[cfg(feature = "plugin")]
         bind_command!(Register);
 
+        #[cfg(feature = "fetch")]
+        bind_command!(Fetch);
+
         // This is a WIP proof of concept
         // bind_command!(ListGitBranches, Git, GitCheckout, Source);