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

從 _HiveClient 及其現有的 hive.kerberos-authentication 路徑開始，然後檢查 TSaslClientTransport 的設定方式。當 DIGEST-MD5 從 $HADOOP_TOKEN_FILE_LOCATION 讀取 Hadoop Writable credentials，並使用 token 識別碼和密碼進行 HMS 驗證時，工作就完成了。

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