[coverage] Conformance findings: CLOUDFETCH-017 #471

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.

• CLOUDFETCH-017: Thrift CloudFetch download failure loses its cause: after the chunk-download retry budget is exhausted on a persistent HTTP 500, the caller receives a bare "Max retry count exceeded" that identifies neither the chunk/result download nor the failed GET's HTTP status (SEA/kernel correctly surfaces "HTTP 500: Internal Server Error")

Reference driver PR: databricks/databricks-sql-go#417
Coverage PR (reproducing xfail tests): https://github.com/databricks/databricks-driver-test/pull/1014