feat: upgrade overlays to support merging namespaces

lib/attrs/default.nix

@@ -7,10 +7,12 @@ let
   inherit (core-inputs.nixpkgs.lib)
     assertMsg
     mapAttrsToList
+    mapAttrs
     flatten
-    fold
+    foldl
     recursiveUpdate
-    mergeAttrs;
+    mergeAttrs
+    isDerivation;
 in
 {
   attrs = {
@@ -25,12 +27,33 @@ in
     # Type: [Attrs] -> Attrs
     # Usage: merge-deep [{ x = 1; } { x = 2; }]
     #   result: { x = 2; }
-    merge-deep = fold recursiveUpdate { };
+    merge-deep = foldl recursiveUpdate { };
 
     # Merge the root of a list of attribute sets.
     # Type: [Attrs] -> Attrs
     # Usage: merge-shallow [{ x = 1; } { x = 2; }]
     #   result: { x = 2; }
-    merge-shallow = fold mergeAttrs { };
+    merge-shallow = foldl mergeAttrs { };
+
+    # Merge shallow for packages, but allow one deeper layer of attribute sets.
+    # Type: [Attrs] -> Attrs
+    # Usage: merge-shallow-packages [ { inherit (pkgs) vim; some.value = true; } { some.value = false; } ]
+    #   result: { vim = ...; some.value = false; }
+    merge-shallow-packages = items:
+      foldl
+        (result: item:
+          result // (mapAttrs
+            (name: value:
+              if isDerivation value then
+                value
+              else if builtins.isAttrs value then
+                (result.${name} or { }) // value
+              else
+                value
+            )
+            item)
+        )
+        { }
+        items;
   };
 }