ArrowCursor converts GetQueryResults fallback values twice in the fetch methods

[laughingman7743]

Problem

With managed query result storage (no S3 output location), ArrowCursor builds its table from GetQueryResults rows that _fetch_all_rows() has already converted with DefaultTypeConverter, and then AthenaArrowResultSet._fetch() converts every value again with self.converters (pyathena/arrow/result_set.py, _as_arrow_from_api() and _fetch()).
The Arrow converters expect strings, so the fetch methods fail or decode twice.

Measured on master 785be36 (2026-10-03) with the managed work group, fetchone() after execute():

Query	Result
SELECT DATE '2026-10-03'	(datetime.date(2026, 10, 3),)
SELECT DECIMAL '1.25'	(Decimal('1.25'),)
SELECT CAST('12:34:56' AS TIME)	TypeError: strptime() argument 1 must be str, not datetime.time
SELECT X'0102'	TypeError: a bytes-like object is required, not 'str'
SELECT json_parse('{"a":1}')	TypeError: the JSON object must be str, bytes or bytearray, not dict
SELECT CAST('{"a":1}' AS JSON)	({'a': 1},), while as_arrow() holds the string '{"a":1}' (decoded twice)

Affected since managed query result storage support was added in v3.28.0 (83566ef, #664).
PolarsCursor had the same double conversion and was fixed in #1005.

Expected

On the GetQueryResults fallback, the fetch methods return the values that as_arrow() holds, without converting them again.

Found while measuring #1018.