utmp Format

[support]

I've noticed a difference in the size of the `utmp` struct between Linux 
6.1.0-22-amd64 and 6.1.0-23-cloud-arm64.  No doubt there are differences 
between other unices as well.  Is there a reason this is still a binary 
log?  On 6.1.0-22-amd64, it seems to be 384 bytes long, while the 
average line length from `utmpdump` is only 125 bytes, so it's not a 
space savings.

My primary concern is forensics.  There is no consistent and reliable 
way to read wtmp/btmp outside of the installation that created it.

JS