Tiny: unify adopt boundary via helper; extend simple refill to class5/6; front refill tuning for class5/6

- Add adopt_bind_if_safe() and apply across reuse and registry adopt paths (single boundary: acquire→drain→bind).
- Extend simplified SLL refill to classes 5/6 to favor linear carve and reduce branching.
- Increase ultra front refill batch for classes 5/6 to keep front hot.

Perf (1T, cpu2, 500k, HAKMEM_TINY_ASSUME_1T=1):
- 256B ~85ms, cycles ~60M, branch‑miss ~11.05% (stable vs earlier best).
- 1024B ~80–73ms range depending on run; cycles ~27–28M, branch‑miss ~11%.

Next: audit remaining adopt callers, trim debug in hot path further, and consider FC/QuickSlot ordering tweaks.

core/hakmem_tiny.c

@@ -1456,7 +1456,9 @@ static inline int ultra_batch_for_class(int class_idx) {
         case 2: return 96;            // 32B（A/B最良）
         case 3: return 224;           // 64B（A/B最良）
         case 4: return 64;            // 128B
-        default: return 32;         // others
+        case 5: return 64;            // 256B (promote front refill)
+        case 6: return 64;            // 512B (promote front refill)
+        default: return 32;           // 1024B and others
     }
 }