Modify nano::locked to work in const contexts (#4846) #2649

Job	Run time
Linux [UBSAN] [lmdb \| clang]	41m 9s
macOS [UBSAN] [lmdb \| clang]	34m 30s
Linux [ASAN] [lmdb \| clang]	39m 6s
macOS [ASAN] [lmdb \| clang]	30m 49s
Linux [ASAN_INT] [lmdb \| clang] (Errors Ignored)	43m 4s
macOS [TSAN] [lmdb \| clang]	33m 0s
Linux [TSAN] [lmdb \| clang]	44m 1s
macOS [UBSAN] [rocksdb \| clang]	44m 41s
Linux [LEAK] [lmdb \| clang]	40m 25s
macOS [ASAN] [rocksdb \| clang]	39m 12s
Linux [UBSAN] [rocksdb \| clang]	48m 15s
Linux [ASAN] [rocksdb \| clang]	55m 17s
macOS [TSAN] [rocksdb \| clang]	50m 10s
Linux [ASAN_INT] [rocksdb \| clang] (Errors Ignored)	55m 44s
Linux [LEAK] [rocksdb \| clang]	55m 37s
	10h 55m 0s

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