[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

從 BaseAllocator 類別開始，檢視 Apache Arrow PR 37723 中參照的 nullability 工作。識別與 DEBUG 相關的欄位，並確定應如何將它們分組到一個私有靜態內部類別中。完成的標準是在不變更預期配置器行為的情況下實作所要求的分離。

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