Fix panic caused by improperly aligned read

[timtom-dev]

Under certain circumstances, Vello could attempt an improperly aligned read, which would cause bytemuck to panic.

This uses bytemuck::pod_read_unaligned instead of bytemuck::from_bytes to achieve the same thing without the possibility of a panic.

[DJMcNab]

Thanks!

To clarify for future readers, the reason we haven't seen this before is that it only happens with an allocator which doesn't inadvertently over-align, which the default allocators on most platforms do.