[Java][Memory][Core]: Initialize DEBUG variable in BaseAllocator class separately

### Describe the enhancement requested

As we were implementing Java Nullability in https://github.com/apache/arrow/pull/37723, we found that there are many variables that are all tied to the DEBUG variable.

Request: Improve the nullability code by creating a new private static inner class to hold all the fields.

### Component(s)

Java

从 BaseAllocator 类开始，检查 Apache Arrow PR 37723 中引用的 nullability 工作。识别与 DEBUG 相关的字段，并确定应如何将它们归组到一个私有静态内部类中。完成的标准是，在不改变预期分配器行为的情况下实现所要求的分离。

由索引模型根据 Issue 内容生成。