feat: Do not depend on user config | Fix merging of configs

because it is a user config, so our config shoudn't break even we if dont have it

use our own table merge function

move loading config to a function

use a global variable to store the config, so no need to call the table function everytime

lua/chadrc.lua

@@ -144,6 +144,4 @@ M.mappings = {
    },
 }
 
-M = vim.tbl_deep_extend("force", require "default_config", M)
-
 return M