fix(providers): no top_p n and temperature for -codex gpt models

* providers - no top_p n and temperature for -codex gpt models

* Update lua/CopilotChat/config/providers.lua

* Update lua/CopilotChat/config/providers.lua

---------

Co-authored-by: Tomas Slusny <slusnucky@gmail.com>

Author: kolchurinvv

lua/CopilotChat/config/providers.lua

@@ -278,6 +278,7 @@ end
 ---@return table
 local function prepare_chat_input(inputs, opts)
   local is_o1 = vim.startswith(opts.model.id, 'o1')
+  local is_codex = opts.model.id:find('codex') ~= nil
 
   inputs = vim.tbl_map(function(input)
     local output = {
@@ -324,7 +325,7 @@ local function prepare_chat_input(inputs, opts)
     end, opts.tools)
   end
 
-  if not is_o1 then
+  if not is_o1 and not is_codex then
     out.n = 1
     out.top_p = 1
     out.temperature = opts.temperature