Ledger: Use representative for change blocks and epoch signer for epoch blocks in linked_account #2635

Job	Run time
macOS [UBSAN] [lmdb \| clang]	33m 40s
Linux [UBSAN] [lmdb \| clang]	43m 34s
macOS [ASAN] [lmdb \| clang]	26m 31s
Linux [ASAN] [lmdb \| clang]	39m 7s
macOS [TSAN] [lmdb \| clang]	32m 22s
Linux [ASAN_INT] [lmdb \| clang] (Errors Ignored)	43m 8s
macOS [UBSAN] [rocksdb \| clang]	40m 37s
Linux [TSAN] [lmdb \| clang]	40m 40s
macOS [ASAN] [rocksdb \| clang]	37m 20s
Linux [LEAK] [lmdb \| clang]	38m 46s
macOS [TSAN] [rocksdb \| clang]	47m 51s
Linux [UBSAN] [rocksdb \| clang]	49m 23s
Linux [ASAN] [rocksdb \| clang]	53m 58s
Linux [ASAN_INT] [rocksdb \| clang] (Errors Ignored)	56m 35s
Linux [LEAK] [rocksdb \| clang]	56m 30s
	10h 40m 2s

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