fix stuck reassign actor

[vporyadke]

Changelog entry

fix an issue where autobalancing could stop after manual group reassign #28194

Changelog category

• Bugfix

Description for reviewers

Пару раз (странно, что не постоянно) наблюдали, что после реассайна остаются висящие акторы, а пока висят акторы мы не запускаем балансер. Чиню зависание если запрос пришёл на реассайн несуществующей таблетки - а это вполне реальный кейс, потому что она могла удалиться с тех пор, как мы сделали query.

[github-actions]

🟢 2025-11-04 10:16:29 UTC The validation of the Pull Request description is successful.

[Copilot]

Pull Request Overview

This PR refactors the TReassignTabletWaitActor class to prevent premature completion and improve code organization. The key change is moving from a pre-calculated total count to an incremental approach where tablets are added individually, and completion is checked dynamically.

• Initializes TabletsTotal to 0 instead of max() to avoid overflow issues
• Introduces AddTablet() method to encapsulate the registration logic and increment the counter
• Adds CheckCompletion() method to centralize completion checking logic

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[github-actions]

⚪ 2025-11-04 10:19:34 UTC Pre-commit check linux-x86_64-relwithdebinfo for ca051a3 has started.
⚪ 2025-11-04 10:19:49 UTC Artifacts will be uploaded here
⚪ 2025-11-04 10:21:13 UTC ya make is running...
🟡 2025-11-04 11:46:46 UTC Some tests failed, follow the links below. Going to retry failed tests...

Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
39125	36287	0	4	2807	27

⚪ 2025-11-04 11:46:59 UTC ya make is running... (failed tests rerun, try 2)
🟢 2025-11-04 11:58:11 UTC Tests successful.

Ya make output | Test bloat | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
82 (only retried tests)	69	0	0	0	13

🟢 2025-11-04 11:58:16 UTC Build successful.
🟢 2025-11-04 11:58:35 UTC ydbd size 2.3 GiB changed* by +208 Bytes, which is < 100.0 KiB vs main: OK

ydbd size dash	main: 802fb8a	merge: ca051a3	diff	diff %
ydbd size	2 429 287 080 Bytes	2 429 287 288 Bytes	+208 Bytes	+0.000%
ydbd stripped size	516 135 944 Bytes	516 135 944 Bytes	0 Bytes	0.000%

^{*please be aware that the difference is based on comparing your commit and the last completed build from the post-commit, check comparation}

[github-actions]

⚪ 2025-11-04 10:19:36 UTC Pre-commit check linux-x86_64-release-asan for ca051a3 has started.
⚪ 2025-11-04 10:19:55 UTC Artifacts will be uploaded here
⚪ 2025-11-04 10:21:23 UTC ya make is running...
🟡 2025-11-04 12:31:22 UTC Some tests failed, follow the links below. This fail is not in blocking policy yet

Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
15532	15056	0	150	300	26

🟢 2025-11-04 12:31:53 UTC Build successful.
🟢 2025-11-04 12:32:20 UTC ydbd size 3.8 GiB changed* by +104 Bytes, which is < 100.0 KiB vs main: OK

ydbd size dash	main: 802fb8a	merge: ca051a3	diff	diff %
ydbd size	4 068 675 512 Bytes	4 068 675 616 Bytes	+104 Bytes	+0.000%
ydbd stripped size	1 510 375 912 Bytes	1 510 375 848 Bytes	-64 Bytes	-0.000%

^{*please be aware that the difference is based on comparing your commit and the last completed build from the post-commit, check comparation}

[CyberROFL]

Можно ли добавить тест?