docs: fix threading module documentation discrepancies

- Fix SpinLock docs: clarify lock()/unlock()/try_lock() are non-const
  (matching source implementation in SpinLock.h)
- Add missing LambdaTask::Execute() method to inherited methods table
- Update TaskGroup::Wait() docs: clarify m_pendingCount never decrements
  causing indefinite block even after all tasks complete (not just
  unexecuted tasks)
- Update TaskGroup::IsComplete() docs: document same m_pendingCount
  issue causing incorrect return values

docs/api/threading/lambdatask/lambdatask.md

@@ -24,6 +24,12 @@
 |------|------|
 | [`LambdaTask`](constructor.md) | 构造 Lambda 任务 |
 
+## 继承方法
+
+| 方法 | 描述 |
+|------|------|
+| `Execute()` | 执行封装的可调用对象（继承自 ITask，可重写） |
+
 ## 使用示例
 
 ```cpp