Improve xtask

[fogti]

Similar to what I did for the xtask of the kernel.

[mkroening]

What is the motivation for making xtask ci optional here? This is not something that users are supposed to build frequently, unlike their application, and thus the kernel.

In any case, please make feature = "ci" a default feature and revert the workflow changes.

Regarding the second commit: I prefer the way it was before, except for

@@ -97,7 +84,7 @@ impl CmdExt for Cmd<'_> {
 
        fn target_dir_args(self, artifact: &Artifact) -> Self {
                if let Some(target_dir) = &artifact.target_dir {
-                       self.args::<&[&OsStr]>(&["--target-dir".as_ref(), target_dir.as_ref()])
+                       self.arg("--target-dir").arg(target_dir)
                } else {
                        self
                }

[fogti]

May I ask what the weird "trip" trough Artifact::profile(&self) == "dev" is supposed to do?

[fogti]

This PR would make thus make it possible to reduce the build time for the release workflow, and also reduces the deps for running cargo xtask clippy (via cargo run --no-default-features -p xtask clippy) locally.