@type file_content() :: binary() | Path.t() | File.Stream.t() | iodata()

@type file_tuple() ::
  {String.t() | nil, file_content()}
  | {String.t() | nil, file_content(), String.t() | nil}
  | {String.t() | nil, file_content(), String.t() | nil, headers()}

@type file_types() :: file_content() | file_tuple()

@type header_kv() :: {binary(), binary()}

@type headers() :: %{optional(binary()) => binary()} | [header_kv()]

@type request_files() ::
  %{optional(String.t()) => file_types()} | [{String.t(), file_types()}]