[coverage] Conformance findings: DATATYPE-041,STATEMENT-023 #470

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.

• DATATYPE-041: SEA backend reports an untyped NULL (VOID) column as TTypeId 16 (NULL) instead of the server-reported STRING type; the same query on Thrift correctly reports STRING, so the column type a caller sees depends on the transport
• STATEMENT-023: SEA backend reports no affected-row count for real DML (numModifiedRows absent for a 3-row INSERT and a 2-row UPDATE) while Thrift reports 3 and 2; absent is returned for every statement alike, so a caller cannot distinguish a real modified-row count from "no count available"

Reference driver PR: databricks/databricks-sql-go#416
Coverage PR (reproducing xfail tests): https://github.com/databricks/databricks-driver-test/pull/1010