`DynamicMessage` deallocates aligned storage with the wrong layout, causing UB

[coolcmyk]

steps to reproduce:

cargo new repro
cd repro
#paste the code below as main.rs
rustup toolchain install nightly --component miri
cargo +nightly miri run

use std::alloc::{Layout, alloc_zeroed, handle_alloc_error};

//see ros2_rust/rclrs/src/dynamic_message.rs:293-302
//for this bug's POC reference
fn buggy_aligned_box(size: usize) -> Box<[u8]> {
    let layout = Layout::from_size_align(size, 8).unwrap();

    unsafe {
        let ptr = alloc_zeroed(layout);

        if ptr.is_null() {
            handle_alloc_error(layout);
        }

        let slice = std::ptr::slice_from_raw_parts_mut(ptr, size);
        Box::from_raw(slice)
    }
}

fn main() {
    let storage = buggy_aligned_box(64);

    // Box<[u8]> deallocates using size 64, alignment 1.
    // well there's no explicit drop written anywhere else,
    // it's just implicitly inserted by rust by the end of the scope.
    drop(storage);
}

[coolcmyk]

I'm currently working on this, will update the WIP state on my branch in the near time