Add support for ILBM

[KateMorley]

This PR adds support for the ILBM (Interleaved Bitmap) format, also known as IFF (which is the container format used by ILBM). ILBM was the main image format used on the Amiga, and is still supported as a save format by Photoshop to this day.

[Roughsketch]

Thanks for the PR, I'll try to review when I have time.

[Roughsketch]

Have a few things that might need to be looked at.

[Roughsketch]

Thank you very much for addressing the changes! I'll do another pass when I can and probably get this merged soon. After it's merged I'll still be waiting on the other open PRs to get resolved, but this will be out in 0.13.0.

[Roughsketch]

Ran a quick fuzzer pass and the following input crashes:

46 4F 52 4D 30 30 30 30 49 4C 42 4D 73 31 73 3D FF FF FF FF

Issue seems to be adding with overflow (4294967295 + 1).

There is similar code in the JXL parser you can use as reference:

let box_end = box_start
    .checked_add(box_size)
    .ok_or(ImageError::CorruptedImage)?;

I will be away for a while, but will run another fuzzer pass after this is resolved.

[KateMorley]

Ran a quick fuzzer pass and the following input crashes:

46 4F 52 4D 30 30 30 30 49 4C 42 4D 73 31 73 3D FF FF FF FF

A chunk with length u32::MAX caused an overflow when adding the padding byte to determine the number of bytes to skip. I’ve fixed it to cast to u64 before the addition rather than after.

[Roughsketch]

Thanks, looks good to me!