25-1-4: schemeshard stats processing opt 0

[ijon]

Cherry-pick:

• 6fefb4b from schemeshard: stats processing optimizations #27165.

Replace calls to PathShardsLimit() and ShardsLimit() with equivalent code.

PathShardsLimit() performs pedantic validation of the path's current shards count by recalculating it through iteration over ShardInfos of the entire database and matching them to the path (!). See CollectAllShards(). That is unreasonable and too slow for the hot spot that is PersistSingleStats(). (Though appropriate for slow paths like TSubOperation::Propose() etc.)

Replacing PathShardsLimit() also eliminates additional TPath construction and hashmap lookup.

[github-actions]

⚪ 2025-10-23 14:51:57 UTC Pre-commit check linux-x86_64-release-asan for af3959d has started.
⚪ 2025-10-23 14:52:13 UTC Artifacts will be uploaded here
⚪ 2025-10-23 14:55:13 UTC ya make is running...
🟡 2025-10-23 16:16:52 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?
12807	12581	0	74	113	39

⚪ 2025-10-23 16:18:12 UTC ya make is running... (failed tests rerun, try 2)
🟡 2025-10-23 16:47:42 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?
284 (only retried tests)	245	0	1	6	32

⚪ 2025-10-23 16:47:51 UTC ya make is running... (failed tests rerun, try 3)
🟡 2025-10-23 17:16:24 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?
64 (only retried tests)	25	0	1	6	32

🟢 2025-10-23 17:16:31 UTC Build successful.
🟢 2025-10-23 17:16:55 UTC ydbd size 3.8 GiB changed* by +2.7 KiB, which is < 100.0 KiB vs stable-25-1-4: OK

ydbd size dash	stable-25-1-4: 5b25abe	merge: af3959d	diff	diff %
ydbd size	4 043 714 432 Bytes	4 043 717 224 Bytes	+2.7 KiB	+0.000%
ydbd stripped size	1 407 719 992 Bytes	1 407 720 696 Bytes	+704 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]

⚪ 2025-10-23 14:51:57 UTC Pre-commit check linux-x86_64-relwithdebinfo for af3959d has started.
⚪ 2025-10-23 14:52:12 UTC Artifacts will be uploaded here
⚪ 2025-10-23 14:55:08 UTC ya make is running...
🟡 2025-10-23 16:05:57 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?
26975	25679	0	6	1239	51

⚪ 2025-10-23 16:08:20 UTC ya make is running... (failed tests rerun, try 2)
🟡 2025-10-23 16:33:51 UTC Some tests failed, follow the links below. Going to retry failed tests...

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

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
114 (only retried tests)	66	0	1	5	42

⚪ 2025-10-23 16:34:00 UTC ya make is running... (failed tests rerun, try 3)
🔴 2025-10-23 16:58:43 UTC Some tests failed, follow the links below.

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

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
77 (only retried tests)	34	0	1	5	37

🟢 2025-10-23 16:58:49 UTC Build successful.
🟢 2025-10-23 16:59:08 UTC ydbd size 2.2 GiB changed* by +1.7 KiB, which is < 100.0 KiB vs stable-25-1-4: OK

ydbd size dash	stable-25-1-4: 5b25abe	merge: af3959d	diff	diff %
ydbd size	2 323 798 112 Bytes	2 323 799 888 Bytes	+1.7 KiB	+0.000%
ydbd stripped size	487 119 488 Bytes	487 119 808 Bytes	+320 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]

🟢 2025-10-23 18:48:57 UTC The validation of the Pull Request description is successful.