crc32c is a runtime dependency

According to https://gitlab.com/kraxel/virt-firmware/-/blob/4a3b4220795716eb50e94df27514719163bc0381/virt/firmware/varstore/aws.py#L17 crc32c should be a runtime dependency or at least an optional dependency of this project.

Is there a reason why there is a custom implementation in virt/firmware/misc.py?