nixos/malloc: add mimalloc

nixos/modules/config/malloc.nix

@@ -30,6 +30,15 @@ let
         vulnerabilities, while maintaining good performance.
       '';
     };
+
+    mimalloc = {
+      libPath = "${pkgs.mimalloc}/lib/libmimalloc.so";
+      description = ''
+        A compact and fast general purpose allocator, which may
+        optionally be built with mitigations against various heap
+        vulnerabilities.
+      '';
+    };
   };
 
   providerConf = providers.${cfg.provider};