## Add Server-Side Cursor/Streaming Support to `adbc_driver_postgresql.dbapi`

[2sls]

What feature or improvement would you like to see?

Add Server-Side Cursor/Streaming Support to adbc_driver_postgresql.dbapi

Maybe I'm missing soemthing, but I’m hitting memory issues with large PostgreSQL queries in adbc_driver_postgresql.dbapi because it fetches full result sets upfront. PostgreSQL supports server-side cursors (DECLARE CURSOR, FETCH) for chunked retrieval, but the driver doesn’t use them natively. I’d like streaming or cursor support to process big results as Arrow tables in chunks, avoiding LIMIT/OFFSET.

Current behavior:

with adbc_driver_postgresql.dbapi.connect(uri) as conn:
    cursor = conn.cursor()
    cursor.execute("SELECT * FROM huge_table")
    chunk = cursor.fetchmany(1000)  # Still loads all rows into memory first

Request: Add a chunk_size param or fetch_arrow_stream() to fetch results incrementally, e.g.:

cursor.execute("SELECT * FROM huge_table", chunk_size=1000)
for chunk in cursor.fetch_arrow_stream():
    print(chunk.num_rows)  # 1000 rows at a time

Could leverage libpq cursors or single-row mode. I'm guessing workaround is manual SQL cursors, but that’s clunky.