feat: add dart comment string autocmd

.config/nvim/lua/tovi/core/autocmd.lua

@@ -9,6 +9,12 @@ local aucmd_dict = {
                 vim.opt_local.shiftwidth = 2
             end,
         },
+        {
+            pattern = 'dart',
+            callback = function ()
+                vim.bo.commentstring = '// %s'
+            end
+        },
     },
 
     BufWritePre = {