Refactor snapshot #2659

Job	Run time
openraft-test-bench (nightly)	1m 46s
Build (nightly, bench,serde,bt,singlethreaded)	1m 24s
stores (memstore)	1m 6s
stores (rocksstore)	10m 18s
stores (rocksstore-compat07)	10m 59s
cluster-benchmark (cluster_benchmark)	1m 9s
examples (stable, raft-kv-memstore)	3m 57s
stores (sledstore)	1m 38s
examples (stable, raft-kv-rocksdb)	13m 17s
external-stores (stores/rocksstore-v2)	10m 34s
examples (nightly, raft-kv-memstore)	3m 50s
examples (nightly, raft-kv-rocksdb)	13m 14s
lint	15m 20s
openraft-feature-test (nightly)	1m 31s
openraft-feature-test (nightly, serde)	1m 28s
openraft-test (stable, 0)	5m 5s
tests-feature-test (nightly)	3m 52s
openraft-test (nightly, 30)	4m 36s
openraft-feature-test (nightly, single-term-leader)	1m 9s
tests-feature-test (nightly, single-term-leader)	5m 2s
openraft-test (nightly, 0, single-term-leader)	5m 18s
openraft-feature-test (nightly, single-term-leader,serde,singlethreaded)	1m 37s
tests-feature-test (nightly, loosen-follower-log-revert)	4m 7s
	2h 2m 17s

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