allow trailing characters to fit in the last field

[dragonnn]

With #182 merged it is responsable to assume a response can have a leading , at it end. Example response:

+QIRD: 69\r\n\x01 @\x00\x00\x00\x0c\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x0f\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x05\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x87,

I think it should be fine to completely remove this check for all cases, if that is not desired I can make it use the flag is_trailing_parsing had happen and then check if d.end() should be run.

[dragonnn]

I hit more issues with parsing data from QIRD by some bytes getting interpreted as whitespace, I think it is not worth fixing it in that way in serde_at.
I worked around it by doing a custom serde parser:

#[derive(Clone, Debug, Deserialize)]
pub struct ReceivedData {
    #[serde(deserialize_with = "raw_bytes")]
    pub data: (usize, Box<[u8]>),
}

impl atat::AtatResp for ReceivedData {}

pub fn raw_bytes<'de, D>(deserializer: D) -> Result<(usize, Box<[u8]>), D::Error>
where
    D: Deserializer<'de>,
{
    struct __Visitor<'de> {
        marker: serde::__private::PhantomData<(usize, Box<[u8]>)>,
        lifetime: serde::__private::PhantomData<&'de ()>,
    }
    impl<'de> serde::de::Visitor<'de> for __Visitor<'de> {
        type Value = (usize, Box<[u8]>);
        fn expecting(&self, __formatter: &mut serde::__private::Formatter) -> serde::__private::fmt::Result {
            serde::__private::Formatter::write_str(__formatter, " Box<[u8]>")
        }

        fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
        where
            E: serde::de::Error,
        {
            match v.split_once(|x| x == &b'\r') {
                Some((size, data)) => {
                    let size = core::str::from_utf8(size).unwrap();
                    let size = size.parse::<usize>().unwrap();
                    Ok((size, Box::from(&data[1..])))
                }
                None => {
                    if !v.is_empty() && v[0] == b'0' {
                        Ok((0, Box::from([])))
                    } else {
                        Err(E::invalid_value(Unexpected::Bytes(v), &self))
                    }
                }
            }
        }
    }

    deserializer.deserialize_bytes(__Visitor {
        marker: serde::__private::PhantomData::<(usize, Box<[u8]>)>,
        lifetime: serde::__private::PhantomData,
    })
}