Backlog scan refactoring #2471

Job	Run time
macOS [UBSAN] [lmdb \| clang]	38m 14s
Linux [UBSAN] [lmdb \| clang]	38m 3s
macOS [ASAN] [lmdb \| clang]	31m 38s
Linux [ASAN] [lmdb \| clang]	37m 35s
macOS [TSAN] [lmdb \| clang]	40m 13s
Linux [ASAN_INT] [lmdb \| clang] (Errors Ignored)	38m 45s
macOS [UBSAN] [rocksdb \| clang]	40m 37s
Linux [TSAN] [lmdb \| clang]	39m 30s
macOS [ASAN] [rocksdb \| clang]	35m 30s
Linux [LEAK] [lmdb \| clang]	40m 32s
macOS [TSAN] [rocksdb \| clang]	50m 41s
Linux [UBSAN] [rocksdb \| clang]	46m 47s
Linux [ASAN] [rocksdb \| clang]	53m 41s
Linux [ASAN_INT] [rocksdb \| clang] (Errors Ignored)	56m 12s
Linux [LEAK] [rocksdb \| clang]	53m 4s
	10h 41m 2s

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