097f7f0695ca6e93d6d169691630f0f2ed199951
- Change `rope_tell()` return type from Option<usize> to usize, always returning cursor's absolute position (offset if unmoved). - Update all call sites to remove `.unwrap_or(...)` around `rope_tell()`. - Add new method `<Rope>::truncate(pos)`, replacing `split_off(...).map(|_| ())`. - Refactor FASTA/FASTQ normalizers to use a single mutable write cursor (`wc`) and document the protocol. - Simplify `end_segment()` logic: commit segment with 0x00 if length ≥ k, else reset. - Improve documentation for write-cursor protocol and rope truncation semantics.