Function cgroup_optional_limit_cell 

pub fn cgroup_optional_limit_cell(
    baseline: Option<u64>,
    candidate: Option<u64>,
    ladder: ScaleLadder,
) -> String

Render a baseline → candidate cell for an Option<u64> LIMIT (e.g. memory.max, memory.high, pids.max). None reads as max (no limit) per format_optional_limit; a step from concrete to max between snapshots renders as <value> → max.