[DBAPI2.0] Fix the description attribute

[Tishj]

Fixes https://github.com/duckdblabs/duckdb-internal/issues/1217, duckdb/duckdb#10495

This PR should make a better attempt at implementing https://peps.python.org/pep-0249/#type-objects-and-constructors

We add the required type object sentinels:

• STRING
• NUMBER
• DATETIME
• BINARY
• ROWID (None, as DuckDB doesn't have a way to detect this on a LogicalType)

The objects returned for the type_code of the description is a DuckDBPyType.
The sentinels are of type DBAPITypeObject and are overloaded to be compared with the DuckDBPyType objects.

The constructors listed by the PEP are not added, they could be added in the future.

[evertlammerts]

From the spec it's not clear what type_code is expected to be. Psycopg returns the type's OID and mysql returns a type id, both of which are numbers, but I don't see a good reason to not return a DuckDBPyType...

[evertlammerts]

lgtm!