chore(devshell): Use deploy-rs from nixpkgs for binary caching

flake.nix

@@ -63,7 +63,6 @@
       self,
       nixpkgs,
       sops-nix,
-      deploy-rs,
       ...
     }@inputs:
     let
@@ -78,6 +77,14 @@
           ./configuration/hardware-specific/vm.nix
         ];
       };
+
+      # deploy-rs unfortunately uses an `import nixpkgs`, and its
+      # library functions depend on an instantiated nixpkgs, so we
+      # can't get around multi-nixpkgs-eval.
+      deploy-rs =
+        (inputs.deploy-rs.overlays.default nixpkgs.legacyPackages.${system}
+          nixpkgs.legacyPackages.${system}
+        ).deploy-rs;
     in
     {
       ##################
@@ -159,7 +166,7 @@
 
           packages = nixpkgs.lib.attrValues {
             inherit (sops-nix.packages.${system}) sops-import-keys-hook sops-init-gpg-key;
-            inherit (deploy-rs.packages.${system}) default;
+            inherit (deploy-rs) deploy-rs;
           };
         };