Fix graph shard backends

[n00bcracker]

During fixing graph shard tests I found out wrong processing of zero Timestamp value in graph shard backends.
Also there were differences between local and memory downsampling implementation.
Furthermore, multiple erasures of non-edge elements of deque were non-optimal.

[github-actions]

⚪ 2025-07-04 16:15:04 UTC Pre-commit check linux-x86_64-relwithdebinfo for 57e4402 has started.
⚪ 2025-07-04 16:15:16 UTC Artifacts will be uploaded here
⚫ 2025-07-04 16:15:42 UTC Check cancelled

[github-actions]

⚪ 2025-07-04 16:15:05 UTC Pre-commit check linux-x86_64-release-asan for 57e4402 has started.
⚪ 2025-07-04 16:15:16 UTC Artifacts will be uploaded here
⚫ 2025-07-04 16:15:42 UTC Check cancelled

[github-actions]

⚪ 2025-07-24 13:00:35 UTC Pre-commit check linux-x86_64-relwithdebinfo for b7bb375 has started.
⚪ 2025-07-24 13:00:39 UTC Artifacts will be uploaded here
⚪ 2025-07-24 13:03:51 UTC ya make is running...
🟡 2025-07-24 14:12:43 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?
29298	27861	0	2	1404	31

⚪ 2025-07-24 14:15:20 UTC ya make is running... (failed tests rerun, try 2)
🟢 2025-07-24 14:27:56 UTC Tests successful.

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

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
433 (only retried tests)	360	0	0	49	24

🟢 2025-07-24 14:28:05 UTC Build successful.
🟢 2025-07-24 14:28:27 UTC ydbd size 2.2 GiB changed* by +16.3 KiB, which is < 100.0 KiB vs main: OK

ydbd size dash	main: 2202202	merge: b7bb375	diff	diff %
ydbd size	2 399 743 008 Bytes	2 399 759 736 Bytes	+16.3 KiB	+0.001%
ydbd stripped size	501 794 440 Bytes	501 801 288 Bytes	+6.7 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]

⚪ 2025-07-24 13:00:53 UTC Pre-commit check linux-x86_64-release-asan for b7bb375 has started.
⚪ 2025-07-24 13:00:57 UTC Artifacts will be uploaded here
⚪ 2025-07-24 13:04:18 UTC ya make is running...
🟡 2025-07-24 14:50:47 UTC Some tests failed, follow the links below. This fail is not in blocking policy yet

Test history | Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
14099	13700	0	114	265	20

🟢 2025-07-24 14:52:01 UTC Build successful.
🟢 2025-07-24 14:52:31 UTC ydbd size 3.9 GiB changed* by +22.2 KiB, which is < 100.0 KiB vs main: OK

ydbd size dash	main: 2202202	merge: b7bb375	diff	diff %
ydbd size	4 219 414 424 Bytes	4 219 437 112 Bytes	+22.2 KiB	+0.001%
ydbd stripped size	1 462 207 832 Bytes	1 462 214 680 Bytes	+6.7 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}