Reconcile the close() docstring on description clearing

The docstring framed description becoming None as an accidental divergence from
stdlib while claiming a stdlib-parity goal for the other preserved fields. The
clear is deliberate: rownumber returns None when description is None, so clearing
it is how a closed cursor's rownumber reads None. Say that instead.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: antoineleclair

src/dqlitedbapi/cursor.py

@@ -1556,8 +1556,10 @@ def close(self) -> None:
         body without masking the body's exception. Clears the result-set
         surface (description / _rows / _row_index) but PRESERVES rowcount
         and lastrowid (stdlib parity; SA reads lastrowid lazily after
-        close). arraysize is also kept (it is a config hint). description
-        becoming None is the one divergence from stdlib.
+        close). arraysize is also kept (it is a config hint). Clearing
+        description is deliberate (stdlib and aiosqlite keep it): it drives
+        the rownumber extension's closed-cursor None semantics, since
+        rownumber returns None when description is None.
         """
         # PEP 249 §6.1.2: clear messages first. Suppress AttributeError
         # so close() from __exit__ after a body exception cannot supplant