WhatsApp's wire format node — a compact binary encoding of XML-like structures.
Each node has a tag (string), attributes (map), and content (child nodes or binary data).
@type t() :: %BaileysEx.BinaryNode{ attrs: %{required(String.t()) => String.t()}, content: [t()] | {:binary, binary()} | binary() | nil, tag: String.t() }