time with time zone values differ by cursor, and PandasCursor drops the offset

[laughingman7743]

Problem

The cursors return different values for an Athena time with time zone column, and PandasCursor drops the offset when it reads the result file from S3.

Measured on master 785be36 (2026-10-03) with SELECT CAST('12:34:56.789 +09:00' AS TIME WITH TIME ZONE) AS t:

Cursor	S3 result file	Managed query result storage (GetQueryResults)
Cursor	'12:34:56.789+09:00' (str)	'12:34:56.789+09:00' (str)
PandasCursor	datetime.time(12, 34, 56, 789000) (naive, offset dropped)	'12:34:56.789+09:00' (str)
ArrowCursor	'12:34:56.789+09:00' (str)	fails on the plain TIME column of the same query (separate defect)
PolarsCursor	'12:34:56.789+09:00' (str)	'12:34:56.789+09:00' (str)

• DefaultTypeConverter and the Arrow and Polars converters map time to _to_time but have no time with time zone entry, so those values stay strings (pyathena/converter.py, pyathena/arrow/converter.py, pyathena/polars/converter.py).
• AthenaPandasResultSet._PARSE_DATES includes time with time zone, so read_csv parses it as a timezone-aware datetime, and _trunc_date() then takes .dt.time, which keeps the local clock time and drops the +09:00 offset (pyathena/pandas/result_set.py). The same column from GetQueryResults stays a string, so PandasCursor also disagrees with itself across result storage modes.

Expected

One documented representation for time with time zone across cursors and result storage modes, with no silent loss of the offset. Either keep the string everywhere, or convert to a timezone-aware datetime.time everywhere.

Found during the review of #1005 (#935).