fix tests due to packed issue

[m4b]

assert_eq borrows the packed structs which is now Against The Rules

ref rust-lang/rust#46043

[m4b]

E.g.:

#[derive(Default, Copy, Clone)]
#[repr(packed)]
struct Foo {
    foo: i64,
    bar: u32,
}

impl scroll::ctx::FromCtx<scroll::Endian> for Foo {
    fn from_ctx(bytes: &[u8], ctx: scroll::Endian) -> Self {
        Foo { foo: bytes.cread_with::<i64>(0, ctx), bar: bytes.cread_with::<u32>(8, ctx) }
    }
}

impl scroll::ctx::SizeWith<scroll::Endian> for Foo {
    type Units = usize;
    fn size_with(_: &scroll::Endian) -> Self::Units {
        ::std::mem::size_of::<Foo>()
    }
}

#[test]
fn ioread_api() {
    use std::io::Cursor;
    use scroll::{LE, IOread};
    let bytes_ = [0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0xef,0xbe,0x00,0x00,];
    let mut bytes = Cursor::new(bytes_);
    let foo = bytes.ioread_with::<i64>(LE).unwrap();
    let bar = bytes.ioread_with::<u32>(LE).unwrap();
    assert_eq!(foo, 1);
    assert_eq!(bar, 0xbeef);
    let error = bytes.ioread_with::<f64>(LE);
    assert!(error.is_err());
    let mut bytes = Cursor::new(bytes_);
    let foo_ = bytes.ioread_with::<Foo>(LE).unwrap();
    assert_eq!(foo_.foo, foo);
    assert_eq!(foo_.bar, bar);
}