Add SQL_SS_UDT (-151) handling for SQL Server spatial types, enabling
geography, geometry, and hierarchyid columns to be fetched as raw bytes.

C++ changes (ddbc_bindings.cpp):
- SQLGetData_wrap: SQL_SS_UDT falls through to SQL_BINARY
- SQLBindColumns: SQL_SS_UDT falls through to SQL_BINARY
- FetchBatchData: SQL_SS_UDT falls through to ProcessBinary
- calculateRowSize: SQL_SS_UDT with LOB-size fallback for 0/SQL_NO_TOTAL
- FetchMany_wrap/FetchAll_wrap: SQL_SS_UDT added to LOB detection

Python changes:
- constants.py: SQL_SS_UDT = -151 in ConstantsDDBC enum + get_valid_types()
- cursor.py: SQL_SS_UDT -> SQL_C_BINARY in _get_c_type_for_sql_type,
  SQL_SS_UDT -> bytes in _map_data_type

Tests: 37 tests covering all three spatial types across fetch paths
(fetchone, fetchmany, fetchall, executemany), NULL handling, mixed-column
queries, output converters, description metadata, spatial methods, error
handling, and binary output consistency.