Chore: enable serde feature in example code #4197

Job	Run time
Build (nightly, bench,serde,bt,singlethreaded)	50s
stores (stores/memstore)	57s
openraft-test (stable, 0)	3m 23s
stores (stores/rocksstore)	6m 36s
openraft-test (nightly, 30)	3m 32s
stores (stores/sledstore)	1m 2s
openraft-test (nightly, 0, single-term-leader)	3m 19s
cluster-benchmark (cluster_benchmark)	51s
examples (stable, memstore)	46s
examples (stable, raft-kv-memstore)	2m 39s
lint	12m 24s
examples (stable, raft-kv-memstore-network-v2)	54s
examples (stable, raft-kv-memstore-opendal-snapshot-data)	1m 13s
openraft-feature-test (nightly)	54s
examples (stable, raft-kv-memstore-singlethreaded)	56s
openraft-feature-test (nightly, serde)	52s
examples (stable, raft-kv-rocksdb)	8m 17s
openraft-feature-test (nightly, single-term-leader)	52s
examples (nightly, memstore)	57s
openraft-feature-test (nightly, single-term-leader,serde,singlethreaded)	51s
openraft-test-bench (nightly)	1m 2s
examples (nightly, raft-kv-memstore)	2m 22s
examples (nightly, raft-kv-memstore-network-v2)	1m 8s
examples (nightly, raft-kv-memstore-opendal-snapshot-data)	1m 30s
rt-monoio	45s
tests-feature-test (nightly)	3m 2s
examples (nightly, raft-kv-memstore-singlethreaded)	1m 8s
tests-feature-test (nightly, single-term-leader)	3m 2s
examples (nightly, raft-kv-rocksdb)	12m 41s
tests-feature-test (nightly, loosen-follower-log-revert)	3m 2s
	1h 21m 47s

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