fix: clean up async Table SessionPool acquisition tasks

[dimastark]

Pull request type

• Bugfix

What is the current behavior?

ydb.aio.SessionPool._get_session_from_queue() leaves its Event.wait() task pending after a successful queued acquisition or a timeout. Repeated queued acquisitions therefore accumulate stop-waiter tasks until the pool stops. Cancelling an acquisition can also lose a session that was dequeued just before cancellation.

Issue Number: N/A

What is the new behavior?

Both queue and stop helper tasks are cancelled when unfinished and awaited before acquisition completes, following the existing cleanup pattern in ydb/aio/_utilities.py. A dequeued session abandoned by cancellation is returned with its original queue priority; after shutdown it is destroyed without starting a replacement. The timeout and existing shutdown behavior are preserved.

Nine deterministic unit tests cover repeated queued acquisitions, positive and nonpositive timeouts, cancellation, and shutdown races using a real pool, queues and events with a mocked driver. All nine fail against the original implementation and pass with the fix. The tests are in the existing ydb/table_test.py and require no YDB server.

Other information

Local validation on Python 3.11.16 / macOS:

• tox -e black
• tox -e style
• tox -e mypy — no issues in 108 source files
• tox -e py -- ydb -v — 247 tests passed

Docker integration tests were not run locally.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.72%. Comparing base (b28a9b5) to head (cfd24bb).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #919      +/-   ##
==========================================
+ Coverage   82.68%   82.72%   +0.03%     
==========================================
  Files          99       99              
  Lines       12961    12969       +8     
  Branches     1269     1273       +4     
==========================================
+ Hits        10717    10728      +11     
+ Misses       1793     1791       -2     
+ Partials      451      450       -1     

Flag	Coverage Δ
integration	80.40% <54.54%> (-0.05%)	⬇️
unit	49.84% <95.45%> (+0.63%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
ydb/aio/table.py	81.98% <100.00%> (+1.45%)	⬆️

... and 1 file with indirect coverage changes

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[vgvoleg]

Hi @dimastark, thanks for the contribution! We don’t actively maintain the Table Service API and plan to remove it in the future. Unless this change addresses a specific problem for a user, I’d prefer to leave this part of the code as it is.

As a wise man once said, “Работает - не трогай” 🙂