added pull to open-addressing containers (#309)

* added pull to open-addressing containers

* added pull_tests.cpp

* guarded pull against exceptions in mid init_type construction

include/boost/unordered/detail/foa/table.hpp

@@ -1,6 +1,6 @@
 /* Fast open-addressing hash table.
  *
- * Copyright 2022-2024 Joaquin M Lopez Munoz.
+ * Copyright 2022-2025 Joaquin M Lopez Munoz.
  * Copyright 2023 Christian Mazakas.
  * Copyright 2024 Braden Ganetsky.
  * Distributed under the Boost Software License, Version 1.0.
@@ -495,6 +495,14 @@ public:
     else return 0;
   }
 
+  BOOST_FORCEINLINE init_type pull(const_iterator pos)
+  {
+    BOOST_ASSERT(pos!=end());
+    erase_on_exit e{*this,pos};
+    (void)e;
+    return type_policy::move(type_policy::value_from(*pos.p()));
+  }
+
   void swap(table& x)
     noexcept(noexcept(std::declval<super&>().swap(std::declval<super&>())))
   {