fix: add growth_left for dump and load, to fix the bug that when loading from a phmap which has a lot of deleted slots may cause further inserts to hang

parallel_hashmap/phmap.h

@@ -2283,6 +2283,8 @@ private:
 
     size_t& growth_left() { return std::get<0>(settings_); }
 
+    const size_t& growth_left() const { return std::get<0>(settings_); }
+
     template <size_t N,
               template <class, class, class, class> class RefSet,
               class M, class P, class H, class E, class A>