Function format_gib 

pub fn format_gib(bytes: u64) -> String

Format a byte count as GiB with one decimal, e.g. 17.2 GiB.

GiB rather than GB, because the division is by 1024^3: it matches how every other memory figure in the launch path is computed, and a banner whose numbers disagree with the --cache-ram budget beside them is worse than no banner.