Fix Array::resize_raw() to allow resizing to the length of the array.

[edmonds]

The new_len parameter to Array::resize_raw() is the new length of the contained octets sequence. The documentation for resize_raw() specifies that it is an error for new_len to be larger than the array size, but the current code also returns an error if new_len is equal to the array size.

The following code will cause a panic with octseq 0.5.2, for instance if one were preparing an Array<512> buffer to receive a UDP DNS query message into.

use octseq::{array::Array, EmptyBuilder};

const UDP_DNS_QUERY_MAX_SIZE: usize = 512;

fn main() {
    let mut query_packet = Array::<UDP_DNS_QUERY_MAX_SIZE>::empty();
    query_packet.resize_raw(UDP_DNS_QUERY_MAX_SIZE).unwrap();
}

[partim]

Thank you for the PR! Looks good.