Refactor: fix handling of non-voter leader #2691

Job	Run time
external-stores (stores/rocksstore-v2)	5m 55s
lint	13m 28s
examples (stable, raft-kv-memstore)	3m 23s
cluster-benchmark (cluster_benchmark)	1m 5s
examples (stable, raft-kv-rocksdb)	8m 3s
examples (nightly, raft-kv-memstore)	2m 20s
openraft-test (stable, 0)	3m 4s
openraft-feature-test (nightly)	48s
examples (nightly, raft-kv-rocksdb)	11m 58s
openraft-test (nightly, 30)	3m 12s
openraft-test-bench (nightly)	1m 23s
openraft-feature-test (nightly, serde)	1m 17s
openraft-test (nightly, 0, single-term-leader)	5m 23s
openraft-feature-test (nightly, single-term-leader)	49s
stores (memstore)	44s
openraft-feature-test (nightly, single-term-leader,serde,singlethreaded)	49s
stores (rocksstore)	12m 51s
Build (nightly, bench,serde,bt,singlethreaded)	48s
stores (rocksstore-compat07)	9m 57s
tests-feature-test (nightly)	3m 39s
stores (sledstore)	51s
tests-feature-test (nightly, single-term-leader)	2m 41s
tests-feature-test (nightly, loosen-follower-log-revert)	4m 25s
	1h 38m 53s

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