fix: max_tokens issue with o1 model (#473)

[akilonx]

This pull requests fixes the max_tokens error that users get when they try to use the newer o1 models.

Unsupported parameter: 'max_tokens' is not supported with this model. Use 'max_completion_tokens' instead.

The new o1 series of models deprecate the max_tokens parameter in favor of a new max_completion_tokens parameter and added support for max_completion_tokens on older models as well.

What this PR does is:

1. defaults 'max_tokens' to 'max_completion_tokens'
2. removes 'max_tokens'

[v3ceban]

Api.edits also needs to be changed to enable edit with instructions feature

function Api.edits(custom_params, cb)
  local openai_params = Utils.collapsed_openai_params(Config.options.openai_params)
  local params = vim.tbl_extend("keep", custom_params, openai_params)
  if params.model == "text-davinci-edit-001" or params.model == "code-davinci-edit-001" then
    vim.notify("Edit models are deprecated", vim.log.levels.WARN)
    Api.make_call(Api.EDITS_URL, params, cb)
    return
  end

  if params.model == "o1-preview" or params.model == "o1-mini" then
    -- max_tokens is unsupported for o1 OpenAI models; older models are backward-compatible with max_tokens,
    -- but max_completion_tokens works with all models.
    params.max_completion_tokens = params.max_tokens
    params.max_tokens = nil
    -- o1 models changed "system" message role to "developer", however, current API
    -- only accepts "user" or "assistant". this will probably be fixed in the future.
    for _, message in ipairs(params.messages) do
      if message.role == "system" then
        message.role = "user"
      end
    end
  end

  Api.make_call(Api.CHAT_COMPLETIONS_URL, params, cb)
end