fix: change global config to default option

lua/Trans/core/backend.lua

@@ -1,8 +1,9 @@
 local Trans = require('Trans')
 local M = Trans.metatable('backend')
+local conf = Trans.conf
 
 --- INFO :Parse online engine keys config file
-local path = Trans.conf.dir .. '/Trans.json'
+local path = conf.dir .. '/Trans.json'
 local file = io.open(path, "r")
 
 if file then
@@ -14,19 +15,12 @@ if file then
     end
 
 
-
-    local default_opts = vim.deepcopy(Trans.conf.backend)
     for name, private_opts in pairs(result or {}) do
-        local opts = vim.tbl_extend('keep', Trans.conf.backend[name] or {}, default_opts, private_opts)
-
-        local backend = M[name]
+        local opts = vim.tbl_extend('keep', conf.backend[name] or {}, conf.backend.default, private_opts)
         for k, v in pairs(opts) do
-            if not backend[k] then
-                backend[k] = v
-            end
+            M[name][k] = v
         end
     end
 end
 
-
 return M