Disallow database operations on network IO threads #2480

Job	Run time
macOS [UBSAN] [lmdb \| clang]	35m 15s
macOS [ASAN] [lmdb \| clang]	31m 5s
Linux [UBSAN] [lmdb \| clang]	37m 6s
macOS [TSAN] [lmdb \| clang]	33m 3s
Linux [ASAN] [lmdb \| clang]	40m 2s
macOS [UBSAN] [rocksdb \| clang]	46m 16s
Linux [ASAN_INT] [lmdb \| clang] (Errors Ignored)	38m 59s
macOS [ASAN] [rocksdb \| clang]	44m 26s
Linux [TSAN] [lmdb \| clang]	38m 50s
macOS [TSAN] [rocksdb \| clang]	55m 28s
Linux [LEAK] [lmdb \| clang]	38m 41s
Linux [UBSAN] [rocksdb \| clang]	46m 1s
Linux [ASAN] [rocksdb \| clang]	54m 17s
Linux [ASAN_INT] [rocksdb \| clang] (Errors Ignored)	54m 25s
Linux [LEAK] [rocksdb \| clang]	56m 10s
	10h 50m 4s

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