ParquetMetadataConverter.java is too long

ParquetMetadataConverter is huge and could benefit from splitting into a few smaller classes with well defined responsibilities.

**Reporter**: [Alex Levenson](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=alexlevenson) / @isnotinvain
**Assignee**: [Ashish Singh](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=singhashish) / @SinghAsDev

_{**Note**: *This issue was originally created as [PARQUET-310](https://issues.apache.org/jira/browse/PARQUET-310). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

首先定位 ParquetMetadataConverter.java 并检查其当前职责。在更改结构之前，确定合适的类边界并检查现有的测试覆盖率。完成的标准是将 converter 拆分为职责定义清晰的较小类，但该 issue 未提供具体的测试或验收标准。

由索引模型根据 Issue 内容生成。