Give cursors a PEP 249 closed state and make query and session starts interrupt-safe #1207

Part of #1205 (step 3; see R3 and model 3 there).

Problem

1. Closed cursors keep working. close() (pyathena/result_set.py:1328-1332) closes the result set but does not mark the cursor closed. Fetches after close() return None / [], and execute() works again. PEP 249 says a closed cursor raises an Error for any operation. The sync and asyncio cursors behave the same.
2. Interrupt before polling. A KeyboardInterrupt in the sync on_start_query_execution callback (pyathena/cursor.py:187) is raised before _poll(). kill_on_interrupt therefore never sends StopQueryExecution, and the query keeps running.
3. cancel() races. Out of scope: a cancel() from another thread on the same cursor is unsupported under threadsafety = 2, as decided in Break result sets after failed or cancelled fetches and drop the cross-thread close guards #1206. The documentation example that does it is rewritten in the Break result sets after failed or cancelled fetches and drop the cross-thread close guards #1206 PR.
4. Spark session leak. StartSession catches only Exception (pyathena/spark/common.py:256-265). A KeyboardInterrupt during or after the request leaves the session running, while the calculation start is interrupt-safe.

Reproduction

The stub reproductions are summarized in #1205. They use stubbed Athena clients and no AWS calls.

Environment

• PyAthena master at b2d7aa2
• Python 3.15

Proposed fix (optional)

• Give cursors a closed state. execute(), executemany(), and the fetch methods of a closed cursor raise ProgrammingError, as PEP 249 requires. This is a breaking change for callers that reuse a closed cursor, and the release notes will call it out. A close() from another thread during execute() is unsupported and not handled.
• Start the protected region of kill_on_interrupt once the execution ID exists, so that the start callback is inside it.
• Give the Spark StartSession the same interrupt-safe start as calculations.

Validate with unit tests for the sync, AsyncCursor, asyncio, and Spark cursors.