Unsoundness in `read_packed_fixed`: Unaligned memory access in v0.8.1

[shinmao]

Hi, I import the crate of quick-protobuf v0.8.1 and accidentally trigger the error with read_packed_fixed::<u32>. However, I found that the code shown in crates.io is different from the one on Github. It seems that the code on crates.io is newer than here?

pub fn read_packed_fixed<'a, M>(&mut self, bytes: &'a [u8]) -> Result<&'a [M]> {
        let len = self.read_varint32(bytes)? as usize;
        if self.len() < len {
            return Err(Error::UnexpectedEndOfBuffer);
        }
        let n = len / ::core::mem::size_of::<M>();
        let slice = unsafe {
            ::core::slice::from_raw_parts(
                bytes.get_unchecked(self.start) as *const u8 as *const M,
                n,
            )
        };
        self.start += len;
        Ok(slice)
}

The code allow to set arbitrary type to generic type without trait bound, which could cause to undefined behavior here.
See crate code here: https://docs.rs/crate/quick-protobuf/0.8.1/source/src/reader.rs#443-462