Support DIGEST-MD5 / delegation token authentication for HMS

### Feature Request / Improvement

#### Summary
PyIceberg's HiveCatalog supports Kerberos (GSSAPI) authentication via `hive.kerberos-authentication`, but does not support DIGEST-MD5 SASL authentication with Hadoop delegation tokens. In many production Hadoop environments, pods/containers authenticate to HMS using delegation tokens (read from `$HADOOP_TOKEN_FILE_LOCATION`) rather than Kerberos keytabs. This means PyIceberg's Hive catalog cannot be used in these environments without building a custom client.

#### Proposed Enhancement
Extend `_HiveClient` to support DIGEST-MD5 delegation token auth:
1. Add a new config property (e.g. `hive.metastore.authentication=DIGEST-MD5`)
2. When DIGEST-MD5 is configured, read credentials from `$HADOOP_TOKEN_FILE_LOCATION` (Hadoop Writable credentials format)
3. Use `TSaslClientTransport` with mechanism=DIGEST-MD5 and the extracted token identifier/password

从 _HiveClient 及其现有的 hive.kerberos-authentication 路径开始，然后检查 TSaslClientTransport 的配置方式。当 DIGEST-MD5 从 $HADOOP_TOKEN_FILE_LOCATION 读取 Hadoop Writable credentials，并使用令牌标识符和密码进行 HMS 身份验证时，工作就完成了。

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