fn eql(vm: &mut VM, self_val: Value, args: &Args2) -> VMResult {
    args.check_args_num(1)?;
    Ok(Value::bool(self_val.eql(&vm[0])))
}
eql?(other) -> bool
https://docs.ruby-lang.org/ja/latest/method/Object/i/eql=3f.html
ruruby/src/builtin/object.rs