Snappy Compression: Optimize DirectBuffer handling/release

The snappy compressor keeps buffers around even when they are not actively being used. When the buffer size is large this can lead to a lot of unneeded memory overhead.

**Reporter**: [Dale Richardson](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=tigerquoll) / @tigerquoll

_{**Note**: *This issue was originally created as [PARQUET-167](https://issues.apache.org/jira/browse/PARQUET-167). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

Issue 未提及任何文件或测试。首先定位 Snappy 压缩器及其 DirectBuffer 分配和释放路径，然后跟踪缓冲区在不活动时仍被保留的时机。完成标准是：在不破坏压缩行为的情况下释放不活动的大型缓冲区；如果项目有相关测试，则为该生命周期添加或更新覆盖。

由索引模型根据 Issue 内容生成。