der: add negative `read_nested` tests

[dishmaker]

Note: I think it would be better for SliceReader::read_nested to return errors with relative

ErrorKind::Incomplete {
    expected_len: 3,
    actual_len: 2
},

instead of absolute:

ErrorKind::Incomplete {
    expected_len: 5,
    actual_len: 4
},

At first, it was counter-intuitive for me, when I set length to 02 for tag 31 and error returned actual_len: 4.