Ignore vectors in bad format during SampleKScan

[vitalif]

Changelog category

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Description for reviewers

Проблемы было две:

1. если в таблице с >1 шардом был хотя бы 1 пустой вектор (пустая строка), то даташарды падали с VERIFY - баг актуален только для main, в 25-4 и ранее его не было (в доработках по битовой квантизации)
2. если в таблице с >1 шардом оказывалось значительное количество строк с векторами в некорректном формате (не только пустых, а также некорректной длины), то построение индекса завершалось неудачей - баг был и в более ранних версиях

[github-actions]

🟢 2026-02-20 18:03:24 UTC The validation of the Pull Request description is successful.

[ydbot]

Run Extra Tests

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• Additional args: custom ya make arguments

[github-actions]

⚪ 2026-02-19 15:58:11 UTC Pre-commit check linux-x86_64-relwithdebinfo for b5b7735 has started.
⚪ 2026-02-19 15:58:30 UTC Artifacts will be uploaded here
⚪ 2026-02-19 16:00:50 UTC ya make is running...
🟡 2026-02-19 18:47:58 UTC Some tests failed, follow the links below. Going to retry failed tests...

Details

Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
48525	45076	0	6	3428	15

⚪ 2026-02-19 18:48:19 UTC ya make is running... (failed tests rerun, try 2)
🟢 2026-02-19 18:50:10 UTC Tests successful.

Ya make output | Test bloat | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
205 (only retried tests)	205	0	0	0	0

🟢 2026-02-19 18:50:18 UTC Build successful.
🟢 2026-02-19 18:50:42 UTC ydbd size 2.4 GiB changed* by +4.6 KiB, which is < 100.0 KiB vs main: OK

ydbd size dash	main: 6e3dbcb	merge: b5b7735	diff	diff %
ydbd size	2 574 341 568 Bytes	2 574 346 328 Bytes	+4.6 KiB	+0.000%
ydbd stripped size	542 612 360 Bytes	542 612 872 Bytes	+512 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]

⚪ 2026-02-19 15:58:12 UTC Pre-commit check linux-x86_64-release-asan for b5b7735 has started.
⚪ 2026-02-19 15:58:16 UTC Artifacts will be uploaded here
⚪ 2026-02-19 15:59:46 UTC ya make is running...
🟡 2026-02-19 18:02:58 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?
18616	18577	0	21	7	11

🟢 2026-02-19 18:03:10 UTC Build successful.
🟢 2026-02-19 18:03:42 UTC ydbd size 3.9 GiB changed* by +10.0 KiB, which is < 100.0 KiB vs main: OK

ydbd size dash	main: 6e3dbcb	merge: b5b7735	diff	diff %
ydbd size	4 192 016 976 Bytes	4 192 027 168 Bytes	+10.0 KiB	+0.000%
ydbd stripped size	1 568 437 728 Bytes	1 568 441 056 Bytes	+3.2 KiB	+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}

[vitalif]

Исправил упавший тест, было недоучтённое поведение, добавил тест на валидацию векторов в tx/datashard/build_index

[ydbot]

Backport

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Branch	Run
stable-25-3, stable-25-3-1, stable-25-4, stable-25-4-1
stable-25-4, stable-25-4-1
stable-25-4