refactor(flake): wrap xonsh as a package

lib/default.nix

@@ -1,4 +1,7 @@
-{inputs}: _: _: let
+{
+  inputs,
+  self,
+}: _: _: let
   mkHost = {
     host,
     system,
@@ -36,8 +39,7 @@
           })
         ];
       specialArgs = {
-        inherit inputs;
-        inherit (inputs) self;
+        inherit inputs self;
       };
     };
 in {