feat(helix): use nixd and mypy for pylsp

roles/home/helix.nix

@@ -17,6 +17,8 @@ let
     python-lsp-ruff
     pylsp-rope
     rope
+    mypy
+    pylsp-mypy
   ]);
 in
 {
@@ -26,7 +28,7 @@ in
       helix
       clang-tools
       rust-analyzer
-      nil
+      nixd
       texlab
       nixpkgs-fmt
       shellcheck
@@ -74,10 +76,15 @@ in
         [[language]]
         name = "nix"
         formatter = { command = "nixpkgs-fmt" }
+        language-servers = ["nixd"]
+
+        [language-server.nixd]
+        command = "nixd"
 
         [language-server.pylsp.config.pylsp.plugins]
         ruff = {enabled = true}
         rope = {enabled = true}
+        mypy = {enabled = true}
 
         [[language]]
         name = "bash"