fix CI: Miri compatibility, benchmark shard count

- num_cpus(): use cfg(miri) to return static 4 instead of available_parallelism()
  (Miri doesn't support sched_getaffinity)
- benches: concurrent_insert uses with_shards(t*2) instead of new()
- node tests: use real allocations instead of integer-to-pointer casts
  (Miri strict provenance)

Author: bravo1goingdark

benches/skiplist_bench.rs

@@ -212,7 +212,7 @@ fn bench_concurrent_insert(c: &mut Criterion) {
     for &threads in &[4, 8] {
         group.bench_with_input(BenchmarkId::new("fastskip", threads), &threads, |b, &t| {
             b.iter(|| {
-                let sl = Arc::new(ConcurrentSkipList::new());
+                let sl = Arc::new(ConcurrentSkipList::with_shards(t * 2));
 
                 let mut handles = vec![];
                 for tid in 0..t {

src/lib.rs

@@ -544,9 +544,16 @@ impl std::fmt::Debug for ConcurrentSkipList {
 
 /// Simple CPU count detection.
 fn num_cpus() -> usize {
-    std::thread::available_parallelism()
-        .map(|n| n.get())
-        .unwrap_or(4)
+    #[cfg(miri)]
+    {
+        4
+    }
+    #[cfg(not(miri))]
+    {
+        std::thread::available_parallelism()
+            .map(|n| n.get())
+            .unwrap_or(4)
+    }
 }
 
 // ─── FrozenMemtable ────────────────────────────────────────────────────────────

src/node.rs

@@ -312,12 +312,16 @@ mod tests {
 
     #[test]
     fn test_tower_ptr_basic() {
-        let p = TowerPtr::new(0x1234_5678 as *const u8);
+        // Use a real allocation to avoid integer-to-pointer casts under Miri
+        let dummy = Box::into_raw(Box::new(42u8));
+        let p = TowerPtr::new(dummy);
         assert!(!p.is_null());
-        assert_eq!(p.ptr(), 0x1234_5678 as *const u8);
+        assert_eq!(p.ptr(), dummy);
 
         assert!(TowerPtr::NULL.is_null());
         assert_eq!(TowerPtr::NULL.ptr(), std::ptr::null());
+
+        unsafe { drop(Box::from_raw(dummy)) };
     }
 
     #[test]
@@ -326,7 +330,9 @@ mod tests {
         unsafe {
             init_node(ptr, 2, b"", b"", false, 1);
 
-            let target = TowerPtr::new(0x1000 as *const u8);
+            // Use a real allocation to avoid integer-to-pointer casts under Miri
+            let dummy = Box::into_raw(Box::new(99u8));
+            let target = TowerPtr::new(dummy);
             tower_store(ptr, 0, target);
             assert_eq!(tower_load(ptr, 0), target);
 
@@ -335,6 +341,7 @@ mod tests {
             let atomic = ptr.add(offset).cast::<AtomicU64>();
             assert_eq!((*atomic).load(Ordering::Acquire), target.raw());
 
+            drop(Box::from_raw(dummy));
             std::alloc::dealloc(ptr, layout);
         }
     }