[25-3] Fix snapshot cleanup on ModifyScheme failures during vector index build (#27454)

[vitalif]

Changelog category

• Not for changelog (changelog entry is not required)

Description for reviewers

Cherry-pick of #27581

[github-actions]

🟢 2025-10-27 10:47:16 UTC The validation of the Pull Request description is successful.

[github-actions]

⚪ 2025-10-27 10:47:38 UTC Pre-commit check linux-x86_64-relwithdebinfo for 1f93b9d has started.
⚪ 2025-10-27 10:47:51 UTC Artifacts will be uploaded here
⚪ 2025-10-27 10:51:23 UTC ya make is running...
🟡 2025-10-27 12:35:10 UTC Some tests failed, follow the links below. Going to retry failed tests...

Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
38328	35649	0	6	2651	22

⚪ 2025-10-27 12:38:09 UTC ya make is running... (failed tests rerun, try 2)
🟡 2025-10-27 13:01:41 UTC Some tests failed, follow the links below. Going to retry failed tests...

Ya make output | Test bloat | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
575 (only retried tests)	554	0	3	0	18

⚪ 2025-10-27 13:01:50 UTC ya make is running... (failed tests rerun, try 3)
🟢 2025-10-27 13:17:18 UTC Tests successful.

Ya make output | Test bloat | Test bloat | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
525 (only retried tests)	509	0	0	0	16

🟢 2025-10-27 13:17:26 UTC Build successful.
🟢 2025-10-27 13:17:43 UTC ydbd size 2.3 GiB changed* by +552 Bytes, which is < 100.0 KiB vs stable-25-3: OK

ydbd size dash	stable-25-3: a2e6a53	merge: 1f93b9d	diff	diff %
ydbd size	2 436 645 376 Bytes	2 436 645 928 Bytes	+552 Bytes	+0.000%
ydbd stripped size	521 811 688 Bytes	521 811 880 Bytes	+192 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]

⚪ 2025-10-27 10:48:03 UTC Pre-commit check linux-x86_64-release-asan for 1f93b9d has started.
⚪ 2025-10-27 10:48:18 UTC Artifacts will be uploaded here
⚪ 2025-10-27 10:52:05 UTC ya make is running...
🟡 2025-10-27 13:11:04 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?
15661	15168	0	233	245	15

🟢 2025-10-27 13:12:19 UTC Build successful.
🟢 2025-10-27 13:12:43 UTC ydbd size 3.8 GiB changed* by +840 Bytes, which is < 100.0 KiB vs stable-25-3: OK

ydbd size dash	stable-25-3: a2e6a53	merge: 1f93b9d	diff	diff %
ydbd size	4 055 146 136 Bytes	4 055 146 976 Bytes	+840 Bytes	+0.000%
ydbd stripped size	1 510 581 024 Bytes	1 510 581 376 Bytes	+352 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}