Change fanout to scale by std::log rather than std::sqrt #2618

Job	Run time
Linux [UBSAN] [lmdb \| clang]	39m 14s
macOS [UBSAN] [lmdb \| clang]	37m 4s
Linux [ASAN] [lmdb \| clang]	42m 7s
macOS [ASAN] [lmdb \| clang]	29m 55s
Linux [ASAN_INT] [lmdb \| clang] (Errors Ignored)	44m 4s
macOS [TSAN] [lmdb \| clang]	35m 5s
Linux [TSAN] [lmdb \| clang]	44m 1s
macOS [UBSAN] [rocksdb \| clang]	42m 33s
Linux [LEAK] [lmdb \| clang]	42m 29s
macOS [ASAN] [rocksdb \| clang]	40m 37s
Linux [UBSAN] [rocksdb \| clang]	48m 5s
macOS [TSAN] [rocksdb \| clang]	50m 4s
Linux [ASAN] [rocksdb \| clang]	52m 0s
Linux [ASAN_INT] [rocksdb \| clang] (Errors Ignored)	55m 2s
Linux [LEAK] [rocksdb \| clang]	53m 18s
	10h 55m 38s

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