@type t() :: %Flagsmith.Configuration{
  api_url: String.t(),
  custom_headers: [{String.t(), String.t()}],
  default_flag_handler: function(),
  enable_analytics: boolean(),
  enable_local_evaluation: boolean(),
  environment_key: String.t(),
  environment_refresh_interval_milliseconds: non_neg_integer(),
  request_timeout_milliseconds: non_neg_integer(),
  retries: non_neg_integer()
}