Improve behaviour in corner cases when used shared threads (#19693)

[kruall]

Changelog entry

Enhanced pool scaling when using shared threads and available CPU resources

Changelog category

• Performance improvement

Description for reviewers

...

[github-actions]

🟢 2025-07-07 10:39:01 UTC The validation of the Pull Request description is successful.

[github-actions]

⚪ 2025-07-07 10:39:25 UTC Pre-commit check linux-x86_64-release-asan for 484b3a4 has started.
⚪ 2025-07-07 10:39:36 UTC Artifacts will be uploaded here
⚪ 2025-07-07 10:42:55 UTC ya make is running...
🟡 2025-07-07 12:36:38 UTC Some tests failed, follow the links below. This fail is not in blocking policy yet Going to retry failed tests...

Test history | Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
14663	14533	0	29	65	36

⚪ 2025-07-07 12:37:56 UTC ya make is running... (failed tests rerun, try 2)
🟡 2025-07-07 12:59:26 UTC Some tests failed, follow the links below. This fail is not in blocking policy yet Going to retry failed tests...

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

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
174 (only retried tests)	72	0	9	58	35

⚪ 2025-07-07 12:59:35 UTC ya make is running... (failed tests rerun, try 3)
🟡 2025-07-07 13:19:39 UTC Some tests failed, follow the links below. This fail is not in blocking policy yet

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

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
133 (only retried tests)	40	0	8	50	35

🟢 2025-07-07 13:19:49 UTC Build successful.
🟢 2025-07-07 13:20:18 UTC ydbd size 3.7 GiB changed* by +22.3 KiB, which is < 100.0 KiB vs stable-25-1-2: OK

ydbd size dash	stable-25-1-2: 5c49af9	merge: 484b3a4	diff	diff %
ydbd size	3 925 671 488 Bytes	3 925 694 368 Bytes	+22.3 KiB	+0.001%
ydbd stripped size	1 372 708 560 Bytes	1 372 721 040 Bytes	+12.2 KiB	+0.001%

^{*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]

⚪ 2025-07-07 10:47:40 UTC Pre-commit check linux-x86_64-relwithdebinfo for 484b3a4 has started.
⚪ 2025-07-07 10:47:50 UTC Artifacts will be uploaded here
⚪ 2025-07-07 10:51:08 UTC ya make is running...
🟡 2025-07-07 12:34:53 UTC Some tests failed, follow the links below. Going to retry failed tests...

Test history | Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
28714	26189	0	1	2456	68

⚪ 2025-07-07 12:37:25 UTC ya make is running... (failed tests rerun, try 2)
🟢 2025-07-07 12:59:20 UTC Tests successful.

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

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
132 (only retried tests)	67	0	0	5	60

🟢 2025-07-07 12:59:27 UTC Build successful.
🟢 2025-07-07 12:59:46 UTC ydbd size 2.1 GiB changed* by +5.7 KiB, which is < 100.0 KiB vs stable-25-1-2: OK

ydbd size dash	stable-25-1-2: 5c49af9	merge: 484b3a4	diff	diff %
ydbd size	2 256 785 232 Bytes	2 256 791 072 Bytes	+5.7 KiB	+0.000%
ydbd stripped size	477 635 608 Bytes	477 639 704 Bytes	+4.0 KiB	+0.001%

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