Function format_human_size 

pub fn format_human_size(bytes: u64) -> String

Format a byte count as a human-readable size.

Uses base-10 units: KB (10^3), MB (10^6), GB (10^9).

Examples:

• 0 → "0 B"
• 1023 → "1023 B"
• 1024 → "1.0 KB"
• 1_500_000 → "1.5 MB"
• 2_500_000_000 → "2.5 GB"