//! Access to reference sequences for alignment validation.
//!
//! The mapper needs the forward-strand bytes of a reference to align a read
//! against. piscem's index does not retain reference sequences, so they are
//! supplied through this trait (salmon-index persists and serves them). Keeping
//! it a trait decouples `salmon-map` from the concrete index/store.
/// Provides reference sequences (and decoy status) to the mapper.