flake: simplify legacyPackages definitions

- Remove the `makeNixvimWithModule` module arg.
- Move standalone wrapper definitions to `wrappers.nix`
- Move `nixvimConfiguration` alias to `nixvim-configurations.nix`

flake/default.nix

@@ -10,7 +10,6 @@
     ./flake-modules
     ./ci.nix
     ./lib.nix
-    ./legacy-packages.nix
     ./nixvim-configurations.nix
     ./overlays.nix
     ./packages.nix

flake/legacy-packages.nix

@@ -1,15 +0,0 @@
-{
-  perSystem =
-    {
-      config,
-      makeNixvimWithModule,
-      ...
-    }:
-    {
-      legacyPackages = rec {
-        inherit makeNixvimWithModule;
-        makeNixvim = module: makeNixvimWithModule { inherit module; };
-        nixvimConfiguration = config.nixvimConfigurations.default;
-      };
-    };
-}

flake/nixvim-configurations.nix

@@ -1,10 +1,12 @@
 { self, ... }:
 {
   perSystem =
-    { system, ... }:
+    { config, system, ... }:
     {
       nixvimConfigurations.default = self.lib.evalNixvim {
         inherit system;
       };
+
+      legacyPackages.nixvimConfiguration = config.nixvimConfigurations.default;
     };
 }

flake/wrappers.nix

@@ -8,13 +8,17 @@ let
 in
 {
   perSystem =
-    { system, ... }:
+    { config, system, ... }:
+    let
+      inherit (config.legacyPackages) makeNixvimWithModule;
+    in
     {
-      _module.args = {
+      legacyPackages = {
         makeNixvimWithModule = import ../wrappers/standalone.nix {
           inherit lib self;
           defaultSystem = system;
         };
+        makeNixvim = module: makeNixvimWithModule { inherit module; };
       };
     };