take_from_bytes_cobs error should return the remainder of the buffer

[matoushybl]

When take_from_bytes_cobs fails to deserialize a value or is called on an incomplete COBS frame, it doesn't return the the remainder of the buffer.
In the first case, the buffer now contains a sequence of bytes already decoded with COBS, a zero and a sequence of bytes not yet decoded with COBS. It would be helpful if the method returned the unencoded portion of the buffer back, so that it could be easily handled further.

In the second case when the buffer doesn't contain a whole COBS frame, it'll leave the buffer further unprocessable.

As a workaround for my project, I implemented a thin wrapper around from_bytes_cobs that always returns the remainder of the buffer.
I can create a PR, if this is the right way to do this.

pub fn take_from_slice<'a, T>(buf: &'a mut [u8]) -> (&'a mut [u8], Result<T, Error>)
where
    T: Deserialize<'a>,
{
    let Some(zero_pos) = buf.iter().position(|&b| b == 0) else {
        return (buf, Err(Error::DeserializeUnexpectedEnd));
    };

    let (leading, trailing) = buf.split_at_mut(zero_pos + 1);

    (trailing, postcard::from_bytes_cobs(leading))
}

This is remotely related to: #71 .