Overhaul of `online_reps` class #2539

Job	Run time
Linux [UBSAN] [lmdb \| clang]	39m 23s
macOS [UBSAN] [lmdb \| clang]	36m 7s
Linux [ASAN] [lmdb \| clang]	36m 52s
macOS [ASAN] [lmdb \| clang]	26m 12s
Linux [ASAN_INT] [lmdb \| clang] (Errors Ignored)	37m 45s
macOS [TSAN] [lmdb \| clang]	28m 14s
Linux [TSAN] [lmdb \| clang]	39m 15s
macOS [UBSAN] [rocksdb \| clang]	37m 14s
Linux [LEAK] [lmdb \| clang]	37m 49s
macOS [ASAN] [rocksdb \| clang]	33m 56s
Linux [UBSAN] [rocksdb \| clang]	49m 20s
macOS [TSAN] [rocksdb \| clang]	47m 43s
Linux [ASAN] [rocksdb \| clang]	54m 6s
Linux [ASAN_INT] [rocksdb \| clang] (Errors Ignored)	54m 11s
Linux [LEAK] [rocksdb \| clang]	52m 53s
	10h 11m 0s

Provide feedback