docs: Fix containers module documentation discrepancies

- Array::SetAllocator: Remove reference to non-existent PoolAllocator class
- HashMap::SetAllocator: Remove reference to non-existent GetDefaultAllocator()
- HashMap::Copy/Move: Fix move constructor complexity (O(m_bucketCount), not O(1))
- HashMap::iterator: Remove C++20 structured bindings example
- String: Add missing links for operator+ and operator==/!=

docs/api/containers/hashmap/setallocator.md

@@ -18,8 +18,8 @@ void SetAllocator(Memory::IAllocator* allocator);
 ```cpp
 XCEngine::Containers::HashMap<int, const char*> map;
 
-auto customAllocator = XCEngine::Memory::GetDefaultAllocator();
-map.SetAllocator(customAllocator);
+// 设置自定义分配器（如果使用内存分配器接口）
+// map.SetAllocator(customAllocator);
 ```
 
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