Support message level custom_metadata on DictionaryBatch (IPC Message field)

### Describe the enhancement requested

Analogous to https://github.com/apache/arrow-java/issues/1035 but for DictionaryBatch.

The Arrow IPC format supports Message level `custom_metadata`, see https://arrow.apache.org/docs/format/Columnar.html#custom-application-metadata and https://github.com/apache/arrow/blob/main/format/Message.fbs#L154

The DictionaryBatch in this implementation currently has no support for this field.

將 DictionaryBatch 的實作與 Apache Arrow issue 1035 中的類似工作進行比較，並檢查 IPC Message.fbs 定義中的訊息層級 custom_metadata 欄位。完成標準是 DictionaryBatch 以與 Arrow IPC 格式一致的方式支援該欄位；使用 repository 現有的測試驗證其行為。

由索引模型根據 Issue 內容生成。