Function build_section_with_layout 

pub fn build_section_with_layout(
    entries: &[OidEntry],
    hash: GitHashKind,
    layout: OidLayout,
) -> Result<Vec<u8>>

build_section with the header offset chosen explicitly. The only thing layout changes is header_len and the zero padding after it — the key, row, ordinal and oid arrays are byte-identical in every layout, which is what makes the arms comparable and what aligned_and_compact_are_the_same_index_byte_for_byte asserts.