Move confirmation processing on to worker threads rather than io thre… #1947

Job	Run time
macOS [UBSAN] [lmdb \| clang]	39m 7s
Linux [UBSAN] [lmdb \| clang]	41m 58s
macOS [ASAN] [lmdb \| clang]	30m 28s
Linux [ASAN] [lmdb \| clang]	40m 1s
macOS [TSAN] [lmdb \| clang]	30m 47s
Linux [ASAN_INT] [lmdb \| clang] (Errors Ignored)	41m 33s
macOS [UBSAN] [rocksdb \| clang]	39m 0s
Linux [TSAN] [lmdb \| clang]	43m 17s
macOS [ASAN] [rocksdb \| clang]	38m 35s
Linux [LEAK] [lmdb \| clang] (Errors Ignored)	41m 29s
macOS [TSAN] [rocksdb \| clang]	52m 42s
Linux [UBSAN] [rocksdb \| clang]	46m 3s
Linux [ASAN] [rocksdb \| clang]	51m 19s
Linux [ASAN_INT] [rocksdb \| clang] (Errors Ignored)	53m 21s
Linux [LEAK] [rocksdb \| clang] (Errors Ignored)	50m 35s
	10h 40m 15s

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