artifact_cache: fix leak of old-generation artifacts, when those artifacts are replaced by newer generation computations. artifacts can opaquely hold things like arena pointers, and so when we replace them in the cache, we need to respect the lookup api's provision of create/destroy hooks for the cache, such that the artifacts can be released correctly (using the destroy hook) before being replaced. this is separate from regular eviction.

src/base/base_arena.h

@@ -46,6 +46,9 @@ struct Arena
 #if ARENA_FREE_LIST
   Arena *free_last;
 #endif
+#if ARENA_TABLE_DEBUG
+  struct ArenaTableNode *table_node;
+#endif
 };
 StaticAssert(sizeof(Arena) <= ARENA_HEADER_SIZE, arena_header_size_check);