Phase 3d-B: TLS Cache Merge - Unified g_tls_sll[] structure (+12-18% expected)

Merge separate g_tls_sll_head[] and g_tls_sll_count[] arrays into unified
TinyTLSSLL struct to improve L1D cache locality. Expected performance gain:
+12-18% from reducing cache line splits (2 loads → 1 load per operation).

Changes:
- core/hakmem_tiny.h: Add TinyTLSSLL type (16B aligned, head+count+pad)
- core/hakmem_tiny.c: Replace separate arrays with g_tls_sll[8]
- core/box/tls_sll_box.h: Update Box API (13 sites) for unified access
- Updated 32+ files: All g_tls_sll_head[i] → g_tls_sll[i].head
- Updated 32+ files: All g_tls_sll_count[i] → g_tls_sll[i].count
- core/hakmem_tiny_integrity.h: Unified canary guards
- core/box/integrity_box.c: Simplified canary validation
- Makefile: Added core/box/tiny_sizeclass_hist_box.o to link

Build: ✅ PASS (10K ops sanity test)
Warnings: Only pre-existing LTO type mismatches (unrelated)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

core/hakmem_tiny_refill_p0.inc.h

@@ -270,8 +270,8 @@ static inline int sll_refill_batch_from_ss(int class_idx, int max_take) {
         trc_linear_carve(slab_base, bs, meta, batch, class_idx, &carve);
         trc_splice_to_sll(
             class_idx, &carve,
-            &g_tls_sll_head[class_idx],
-            &g_tls_sll_count[class_idx]);
+            &g_tls_sll[class_idx].head,
+            &g_tls_sll[class_idx].count);
         ss_active_add(tls->ss, batch);
 #if HAKMEM_DEBUG_COUNTERS
         extern unsigned long long g_rf_carve_items[];