[coverage] Conformance findings: SESSION-016 #467

Surfaced by the multi-language coverage fan-out while conformance-testing these SPEC-IDs against databricks/databricks-sql-nodejs.

Each is committed as an expected-failure (xfail) test in the coverage PR — the test asserts the CORRECT behavior and stays red until this driver is fixed.

• SESSION-016: Thrift connection-failure primary message drops the server-provided 401 detail, surfacing only "Received a response with a bad HTTP status code: 401" instead of the server text ("Invalid access token")
• SESSION-016: SEA session-open rejection throws an AuthenticationError with no cause chain (keys=["name"]; no cause/underlying/innerError), so the underlying transport/SDK error is not preserved — the message detail and HTTP status themselves are correct

Reference driver PR: databricks/databricks-jdbc#1587
Coverage PR (reproducing xfail tests): https://github.com/databricks/databricks-driver-test/pull/988