Avoid unnecessary ReadStep coordinator subscriptions

[snaury]

Changelog entry

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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]

⚪ 2025-01-20 13:24:11 UTC Pre-commit check linux-x86_64-relwithdebinfo for dde198c has started.
⚪ 2025-01-20 13:24:26 UTC Artifacts will be uploaded here
⚪ 2025-01-20 13:27:34 UTC ya make is running...
🟡 2025-01-20 14:17:22 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?
18802	17460	0	6	1213	123

⚪ 2025-01-20 14:18:57 UTC ya make is running... (failed tests rerun, try 2)
🟢 2025-01-20 14:30:52 UTC Tests successful.

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

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
230 (only retried tests)	108	0	0	0	122

🟢 2025-01-20 14:30:58 UTC Build successful.
🟢 2025-01-20 14:31:19 UTC ydbd size 2.1 GiB changed* by +7.0 KiB, which is < 100.0 KiB vs main: OK

ydbd size dash	main: 04f4156	merge: dde198c	diff	diff %
ydbd size	2 216 627 368 Bytes	2 216 634 496 Bytes	+7.0 KiB	+0.000%
ydbd stripped size	468 629 104 Bytes	468 630 192 Bytes	+1.1 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}

[github-actions]

⚪ 2025-01-20 13:24:14 UTC Pre-commit check linux-x86_64-release-asan for dde198c has started.
⚪ 2025-01-20 13:24:26 UTC Artifacts will be uploaded here
⚪ 2025-01-20 13:27:26 UTC ya make is running...
🟡 2025-01-20 14:31:14 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?
11379	11325	0	15	9	30

⚪ 2025-01-20 14:32:14 UTC ya make is running... (failed tests rerun, try 2)
🟡 2025-01-20 14:44:13 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?
82 (only retried tests)	51	0	1	4	26

⚪ 2025-01-20 14:44:23 UTC ya make is running... (failed tests rerun, try 3)
🟢 2025-01-20 14:56:07 UTC Tests successful.

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

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
53 (only retried tests)	28	0	0	0	25

🟢 2025-01-20 14:56:14 UTC Build successful.
🟢 2025-01-20 14:56:41 UTC ydbd size 3.6 GiB changed* by +18.0 KiB, which is < 100.0 KiB vs main: OK

ydbd size dash	main: 04f4156	merge: dde198c	diff	diff %
ydbd size	3 852 980 728 Bytes	3 852 999 136 Bytes	+18.0 KiB	+0.000%
ydbd stripped size	1 346 195 888 Bytes	1 346 204 592 Bytes	+8.5 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}