clocksource: add additional methods for coarse duration #397

Job	Run time
audit	10s
clippy	22s
check-ubuntu-latest	17s
build-ubuntu-latest-release	50s
check-macos-latest	52s
rustfmt	5s
build-ubuntu-latest-debug	39s
check-windows-latest	2m 1s
build-macos-latest-release	3m 3s
build-macos-latest-debug	3m 6s
build-windows-latest-release	2m 42s
build-windows-latest-debug	2m 37s
clippy-upload	17s
verify all tests pass	1s
	17m 2s

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