Add consuming k-mer iterators to PackedSeq and Superkmer

Introduces `into_kmers()` and `into_canonical_kmers()` consuming methods to `PackedSeq` and `Superkmer`, enabling zero-allocation sliding-window k-mer extraction via bitwise operations. This complements existing borrow-based iterators by allowing direct ownership transfer. Also includes minor documentation updates, whitespace fixes, and new unit tests to verify canonical k-mer iteration counts and output sequences.

src/obikseq/src/packed_seq.rs

@@ -232,6 +232,18 @@ impl PackedSeq {
         self.iter_kmers().map(|km| km.canonical())
     }
 
+    /// Consuming iterator over all k-mers. Moves `self` into the iterator; zero allocation.
+    #[inline]
+    pub fn into_kmers(self) -> OwnedPackedSeqKmerIter {
+        OwnedPackedSeqKmerIter::new(self)
+    }
+
+    /// Consuming iterator over all canonical k-mers. Moves `self` into the iterator; zero allocation.
+    #[inline]
+    pub fn into_canonical_kmers(self) -> impl Iterator<Item = CanonicalKmer> {
+        self.into_kmers().map(|km| km.canonical())
+    }
+
     /// Extract nucleotides `[start, end)` as a new [`PackedSeq`]. Allocates.
     pub fn sub(&self, start: usize, end: usize) -> Self {
         debug_assert!(end > start && end <= self.seql());
@@ -317,6 +329,51 @@ impl Iterator for PackedSeqKmerIter<'_> {
     }
 }
 
+// ── OwnedPackedSeqKmerIter ────────────────────────────────────────────────────
+
+/// Sliding-window kmer iterator that owns its [`PackedSeq`]. Zero allocation.
+pub struct OwnedPackedSeqKmerIter {
+    seq: PackedSeq,
+    mask: u64,
+    lshift: usize,
+    current: u64,
+    pos: usize,
+    max_pos: usize,
+}
+
+impl OwnedPackedSeqKmerIter {
+    fn new(seq: PackedSeq) -> Self {
+        let seql = seq.seql();
+        let klen = k();
+        let lshift = 64 - klen * 2;
+        let mask = ((!0u128) << (lshift + 2)) as u64;
+        let current = if seql >= klen {
+            seq.extract::<KLen>(0).map(|km| km.raw()).unwrap_or(0)
+        } else {
+            0
+        };
+        Self { seq, mask, lshift, current, pos: klen, max_pos: seql }
+    }
+}
+
+impl Iterator for OwnedPackedSeqKmerIter {
+    type Item = Kmer;
+
+    fn next(&mut self) -> Option<Kmer> {
+        if self.pos > self.max_pos {
+            return None;
+        }
+        let result = Kmer::from_raw(self.current);
+        if self.pos < self.max_pos {
+            let inner_shift = 6 - 2 * (self.pos & 3);
+            let nuc = ((self.seq.seq[self.pos / 4] >> inner_shift) & 3) as u64;
+            self.current = ((self.current << 2) & self.mask) | (nuc << self.lshift);
+        }
+        self.pos += 1;
+        Some(result)
+    }
+}
+
 // ── varint (LEB128) ───────────────────────────────────────────────────────────
 
 pub(crate) fn write_varint<W: Write>(w: &mut W, mut val: u64) -> io::Result<()> {

src/obikseq/src/superkmer.rs

@@ -207,6 +207,12 @@ impl SuperKmer {
     pub fn iter_canonical_kmers(&self) -> impl Iterator<Item = CanonicalKmer> + '_ {
         self.inner.iter_canonical_kmers()
     }
+
+    /// Consuming iterator over all canonical k-mers. Moves `self`; zero allocation.
+    #[inline]
+    pub fn into_canonical_kmers(self) -> impl Iterator<Item = CanonicalKmer> {
+        self.inner.into_canonical_kmers()
+    }
 }
 
 #[cfg(test)]