feat(hpc): add zeck module (ZeckF64 encoding + batch/top_k) and hamming_top_k_raw

New hpc::zeck module ported from lance-graph's ZeckF64 progressive edge encoding:
- zeckf64() / zeckf64_from_distances() — encode SPO triple distances
- zeckf64_distance() / scent_distance() / progressive_distance()
- zeckf64_batch() / zeckf64_top_k() — batch distance + O(n) partial sort
- zeckf64_scent_batch() / zeckf64_scent_top_k() — scent-only fast path
- zeckf64_encode_batch() — encode query against flat database
- is_legal_scent() — boolean lattice validation
- 11 tests passing

Also added hamming_top_k_raw() to hpc::bitwise for raw slice top-k search.

https://claude.ai/code/session_01CdqyUTUfjKZuk8YGJzv6LB

Author: claude

src/hpc/bitwise.rs

@@ -230,6 +230,31 @@ pub fn hamming_batch_raw(query: &[u8], database: &[u8], num_rows: usize, row_byt
     dispatch_hamming_batch(query, database, num_rows, row_bytes)
 }
 
+/// Top-k nearest neighbors by Hamming distance on raw slices.
+///
+/// Returns (indices, distances) of the k closest rows in the database.
+/// Uses `select_nth_unstable` for O(n) partial sort instead of O(n log n).
+pub fn hamming_top_k_raw(
+    query: &[u8],
+    database: &[u8],
+    num_rows: usize,
+    row_bytes: usize,
+    k: usize,
+) -> (Vec<usize>, Vec<u64>) {
+    let distances = dispatch_hamming_batch(query, database, num_rows, row_bytes);
+    let k = k.min(num_rows);
+    if k == 0 {
+        return (Vec::new(), Vec::new());
+    }
+    let mut indexed: Vec<(usize, u64)> = distances.into_iter().enumerate().collect();
+    indexed.select_nth_unstable_by_key(k.saturating_sub(1), |&(_, d)| d);
+    indexed.truncate(k);
+    indexed.sort_unstable_by_key(|&(_, d)| d);
+    let indices = indexed.iter().map(|&(i, _)| i).collect();
+    let dists = indexed.iter().map(|&(_, d)| d).collect();
+    (indices, dists)
+}
+
 fn dispatch_hamming(a: &[u8], b: &[u8]) -> u64 {
     #[cfg(target_arch = "x86_64")]
     {

src/hpc/mod.rs

@@ -126,6 +126,10 @@ pub mod layered_distance;
 #[allow(missing_docs)]
 pub mod parallel_search;
 
+// ZeckF64 progressive edge encoding + batch/top-k
+#[allow(missing_docs)]
+pub mod zeck;
+
 #[cfg(test)]
 mod e2e_tests {
     //! End-to-end pipeline test: Fingerprint → Node → Seal → Cascade → CLAM → Causality → BNN