browserpass: merge home.file entries with mergeAttrsList

The native-messaging host files were combined with a linear foldl' of //,
which recopies the accumulator on every step (O(n^2)). mergeAttrsList does
the same right-biased shallow merge with a balanced binary merge.

modules/programs/browserpass.nix

@@ -32,7 +32,7 @@ in
   };
 
   config = lib.mkIf cfg.enable {
-    home.file = lib.foldl' (a: b: a // b) { } (
+    home.file = lib.mergeAttrsList (
       lib.concatMap (
         x:
         with pkgs.stdenv;