fix: better backend configuration file parser

lua/Trans/core/backend.lua

@@ -0,0 +1,32 @@
+local Trans = require('Trans')
+local M = Trans.metatable('backend')
+
+--- INFO :Parse online engine keys config file
+local path = Trans.conf.dir .. '/Trans.json'
+local file = io.open(path, "r")
+
+if file then
+    local content = file:read("*a")
+    local status, result = pcall(vim.json.decode, content)
+    file:close()
+    if not status then
+        error('Unable to parse json file: ' .. path .. '\n' .. result)
+    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]
+        for k, v in pairs(opts) do
+            if not backend[k] then
+                backend[k] = v
+            end
+        end
+    end
+end
+
+
+return M