Add `coverage_map` crate to provide `CoverageMapBuilder` and `CoverageMap` data structures #52

Job	Run time
build	4m 12s
fmt	3s
clippy	1m 28s
tests (file-store)	1m 44s
tests (ingest)	1m 29s
tests (reward-scheduler)	43s
tests (mobile-packet-verifier)	1m 29s
tests (task-manager)	53s
tests-postgres (iot-config)	2m 17s
tests-postgres (iot-packet-verifier)	3m 1s
tests-postgres (boost-manager)	2m 4s
tests-postgres (iot-verifier)	2m 23s
tests-postgres (mobile-config)	1m 54s
tests-postgres (mobile-verifier)	2m 16s
build-release	0s
	25m 56s

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