chickenPackages: recurse into attrs

This makes chicken packages (eggs) discoverable.

This came up during:

https://github.com/NixOS/nixpkgs/pull/165023#issuecomment-1116655349

pkgs/development/compilers/chicken/4/default.nix

···
       bootstrap-chicken = self.chicken.override { bootstrap-chicken = null; };
     };
 
-    chickenEggs = callPackage ./eggs.nix { };
+    chickenEggs = lib.recurseIntoAttrs (callPackage ./eggs.nix { });
 
     egg2nix = callPackage ./egg2nix.nix { };
   };

pkgs/development/compilers/chicken/5/default.nix

···
       bootstrap-chicken = self.chicken.override { bootstrap-chicken = null; };
     };
 
-    chickenEggs = callPackage ./eggs.nix { };
+    chickenEggs = lib.recurseIntoAttrs (callPackage ./eggs.nix { });
 
     egg2nix = callPackage ./egg2nix.nix { };
   };