fix promotion rewards by encoding timestamp as seconds #441

Job	Run time
build	2m 37s
fmt	14s
clippy	2m 8s
tests (coverage-map)	1m 34s
tests (reward-scheduler)	1m 15s
tests (coverage-point-calculator)	1m 22s
tests (ingest)	1m 57s
tests (task-manager)	54s
tests-postgres (boost-manager)	2m 36s
tests-postgres (file-store)	2m 13s
tests-postgres (iot-config)	2m 28s
tests-postgres (iot-packet-verifier)	4m 0s
tests-postgres (iot-verifier)	2m 34s
tests-postgres (mobile-config)	2m 28s
tests-postgres (mobile-packet-verifier)	2m 37s
tests-postgres (mobile-verifier)	3m 3s
build-release	0s
	34m 0s

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