enable all-features in nix for CI builds

CI is running `cargo build --all-features`, so we should be passing all
the features to nix as well.

The only thing this currently affects is the jemalloc_prof feature, but if
we add any non-default features that affect nix in the future they should
also be handled correctly now.

bin/nix-build-and-cache

@@ -70,7 +70,7 @@ ci() {
         --inputs-from "$toplevel"
 
         # Keep sorted
-        "$toplevel#devShells.x86_64-linux.default"
+        "$toplevel#devShells.x86_64-linux.all-features"
         attic#default
         nixpkgs#direnv
         nixpkgs#jq