PR :SessionPool Fix graceful shutdown by notifying waiting threads in close

[torga the gamer]

Hi all,

I opened a PR #17381 2 weeks ago that fixes a bug in SessionPool.close()
where waiting threads were not being notified on shutdown, causing them to
hang until their wait(1000) timeout expired.

The fix adds a notifyAll() call inside close() so threads blocked in
getSession() are immediately unblocked and throw IoTDBConnectionException.

PR: https://github.com/apache/iotdb/pull/17381

Would appreciate any review.

Thanks you,

Shem.