Chore: enable serde feature in example code #4196

Job	Run time
lint	12m 17s
examples (stable, memstore)	44s
examples (stable, raft-kv-memstore)	2m 36s
openraft-feature-test (nightly)	50s
examples (stable, raft-kv-memstore-network-v2)	57s
openraft-feature-test (nightly, serde)	53s
cluster-benchmark (cluster_benchmark)	47s
openraft-test (stable, 0)	3m 25s
examples (stable, raft-kv-memstore-opendal-snapshot-data)	1m 9s
openraft-feature-test (nightly, single-term-leader)	53s
openraft-test (nightly, 30)	3m 29s
openraft-feature-test (nightly, single-term-leader,serde,singlethreaded)	53s
examples (stable, raft-kv-memstore-singlethreaded)	58s
openraft-test-bench (nightly)	1m 1s
openraft-test (nightly, 0, single-term-leader)	3m 16s
examples (stable, raft-kv-rocksdb)	8m 19s
examples (nightly, memstore)	59s
rt-monoio	41s
Build (nightly, bench,serde,bt,singlethreaded)	54s
examples (nightly, raft-kv-memstore)	2m 23s
examples (nightly, raft-kv-memstore-network-v2)	1m 10s
examples (nightly, raft-kv-memstore-opendal-snapshot-data)	1m 27s
tests-feature-test (nightly)	3m 2s
examples (nightly, raft-kv-memstore-singlethreaded)	1m 11s
stores (stores/memstore)	55s
stores (stores/rocksstore)	6m 9s
examples (nightly, raft-kv-rocksdb)	12m 52s
tests-feature-test (nightly, single-term-leader)	3m 4s
stores (stores/sledstore)	1m 4s
tests-feature-test (nightly, loosen-follower-log-revert)	3m 2s
	1h 21m 20s

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