//! Per-record index entries within a block.
/// A fixed-width index entry for one record within a block.
///
/// Each entry stores byte offsets and lengths into the block's
/// payload sections, allowing constant-time access to any record's
/// fields without scanning the payload data.
///
/// When a section is omitted for the entire block (for example,
/// names or qualities), the corresponding offset and length fields
/// in the index entry are ignored. Section presence is determined
/// by the block header, not by the index.
pub