24-3: Avoid unnecessary ReadStep coordinator subscriptions

[snaury]

Changelog entry

...

Changelog category

• Not for changelog (changelog entry is not required)

Additional information

We use ReadStep subscriptions to restore the maximum version that could have been used in snapshot reads by previous generations. While we need the initial subscription response, we don't actually use ReadStep updates, which end up wasting interconnect capacity at coordinator nodes. Unsubscribe from these updates in datashard and timecast as soon as possible, which is a backwards compatible change. Later we could switch to a more efficient API.

Fixes #13548.

[github-actions]

⚪ 2025-01-21 10:55:06 UTC Pre-commit check for e03ce2a has started.
⚪ 2025-01-21 10:57:51 UTC Build linux-x86_64-release-asan is running...
🟢 2025-01-21 11:24:04 UTC Build successful.
⚪ 2025-01-21 11:24:21 UTC Tests are running...
🔴 2025-01-21 13:35:34 UTC Some tests failed, follow the links below.

Test history | Test log

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
10403	10304	0	28	26	45

🟢 2025-01-21 13:36:31 UTC ydbd size 5.6 GiB changed* by +5.4 KiB, which is < 100.0 KiB vs stable-24-3: OK

ydbd size dash	stable-24-3: fa450dd	merge: e03ce2a	diff	diff %
ydbd size	6 002 533 944 Bytes	6 002 539 448 Bytes	+5.4 KiB	+0.000%
ydbd stripped size	1 504 208 288 Bytes	1 504 209 024 Bytes	+736 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]

⚪ 2025-01-21 10:55:08 UTC Pre-commit check for e03ce2a has started.
⚪ 2025-01-21 10:58:23 UTC Build linux-x86_64-relwithdebinfo is running...
🟢 2025-01-21 11:42:05 UTC Build successful.
⚪ 2025-01-21 11:42:20 UTC Tests are running...
🔴 2025-01-21 13:22:01 UTC Some tests failed, follow the links below.

Test history | Test log

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
14732	13371	0	17	1300	44

🟢 2025-01-21 13:22:57 UTC ydbd size 8.3 GiB changed* by +488 Bytes, which is < 100.0 KiB vs stable-24-3: OK

ydbd size dash	stable-24-3: fa450dd	merge: e03ce2a	diff	diff %
ydbd size	8 874 209 416 Bytes	8 874 209 904 Bytes	+488 Bytes	+0.000%
ydbd stripped size	484 292 552 Bytes	484 292 424 Bytes	-128 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}