lsp: use nvim-metals instead of lsp-config for scala

config/lsp/lsp.nix

@@ -1,4 +1,4 @@
-{ ... }:
+{ helpers, ... }:
 
 {
   plugins.lsp = {
@@ -16,9 +16,6 @@
       nixd = {
         enable = true;
       };
-      metals = {
-        enable = true;
-      };
     };
     inlayHints = true;
     keymaps = {
@@ -73,4 +70,19 @@
       };
     };
   };
+
+  keymaps = [
+    {
+      mode = [ "n" ];
+      key = "<leader>th";
+      action = helpers.mkRaw ''
+        function()
+          vim.lsp.inlay_hint.enable(not vim.lsp.inlay_hint.is_enabled())
+        end
+      '';
+      options = {
+        desc = "Toggle inlay hints";
+      };
+    }
+  ];
 }