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

Start with _HiveClient and its existing hive.kerberos-authentication path, then inspect how TSaslClientTransport is configured. The work is done when DIGEST-MD5 reads the Hadoop Writable credentials from $HADOOP_TOKEN_FILE_LOCATION and uses the token identifier and password for HMS authentication.

Written by the indexing model from the issue text.