fix(tvix): Reuse now exposed depotfmt wrapper in crate2nix-check

This change exposes the already existing wrapper for treefmt/depotfmt
that supports running it inside a sandbox. We now reuse it inside
//tvix/crate2nix-check, where we previously duplicated the code. The
check is now stricter and will also fail on changes, so I had to set the
rust edition in the treefmt config.

Change-Id: I000e52421258979c038ba6b1f1ff2db14e391b0c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12068
Tested-by: BuildkiteCI
Autosubmit: Ilan Joselevich <personal@ilanjoselevich.com>
Reviewed-by: flokli <flokli@flokli.de>

tvix/default.nix

@@ -73,11 +73,8 @@ in
         cargo metadata > /dev/null
 
         ${pkgs.crate2nix}/bin/crate2nix generate --all-features
-        ${pkgs.treefmt}/bin/treefmt Cargo.nix \
-          --no-cache \
-          --on-unmatched=debug \
-          --config-file=${depot.tools.depotfmt.config} \
-          --tree-root=.
+        # Reuse depotfmt wrapper that can be used inside a sandbox.
+        ${depot.tools.depotfmt.check} Cargo.nix
 
         # technically unnecessary, but provides more-helpful output in case of error
         diff -ur Cargo.nix ${src}/Cargo.nix