isExternal function
Returns true if object
is External, otherwise false.
Implementation
bool isExternal(final Map<String, dynamic>? object) {
if (object == null) return false;
if (object[r'$type'] == null) return false;
return object[r'$type'] == 'app.bsky.embed.external#main' ||
object[r'$type'] == 'app.bsky.embed.external';
}