Tighten Error determination

[fregante]

• Part of Enumerable properties are made non-enumerable #84
• Blocked by Require Node.js 18+ #100

This PR:

• stops treating {message} as a deserializable error unless it's specifically:

   {message: string}

• stops treating {name, message, stack} as an error unless it's specifically

   {
   	name: string,
   	message: string,
   	stack: string,
   }

Technically breaking changes, in practice they're just bug fixes.