docs: Fix memory module documentation discrepancies

- Add missing PoolAllocator class overview with methods table
- Add missing LinearAllocator class overview with methods table
- Add missing ProxyAllocator class overview with methods table
- Fix PoolAllocator::Allocate example code and comments
- Clarify ProxyAllocator::Free totalFreed calculation behavior
- Fix CreateLinearAllocator complexity from O(size) to O(1)
- Add note about Reallocate thread safety in ProxyAllocator

docs/api/memory/proxy-allocator/reallocate.md

@@ -4,7 +4,7 @@
 void* Reallocate(void* ptr, size_t newSize) override;
 ```
 
-重新分配内存。调用直接转发到底层分配器，不记录任何统计信息（简化实现）。此方法仅将调用转发给底层分配器。
+重新分配内存。调用转发到底层分配器，不记录额外统计信息（底层分配器的返回值直接返回）。此方法线程安全，内部使用互斥锁保护。
 
 **参数：**
 - `ptr` - 现有内存块指针