Boxify superslab registry, add bench profile, and document C7 hotpath experiments

core/box/ss_allocation_box.c

@@ -284,6 +284,10 @@ SuperSlab* superslab_allocate(uint8_t size_class) {
         }
     } while (0);
 
+    if (!from_cache) {
+        ss_stats_on_ss_alloc_class(size_class);
+    }
+
     return ss;
 }