[coverage] Conformance findings: DATATYPE-040

[peco-engineer-bot]

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

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-040: DECIMAL read as text is rendered in exponent form for sub-1 high-scale values (DECIMAL(20,7) 0.0000001 -> "1E-7") instead of plain decimal notation, garbling the value for text consumers (PECOBLR-2096)

Reference driver PR: https://github.com/databricks/databricks-odbc/pull/134
Coverage PR (reproducing xfail tests): https://github.com/databricks/databricks-driver-test/pull/997