🗑️ Refactor entropy and minimizer logic into RollingStat

- Remove `entropy.rs`, `minimizer.rs` and `window.rs`; consolidate logic into new module
- Introduce unified state management in RollingStat with incremental entropy tracking and canonical minimizer computation via monotone deque
- Update SuperKmerIter to use RollingStat instead of separate components, simplifying iteration and state transitions
- Add `*.fasta` to .gitignore for generated FASTA outputs

.gitignore

@@ -1,3 +1,4 @@
 .venv/
 src/target
 data-stress
+*.fasta