ringlog: make metrics optional (#118) #431

Job	Run time
audit	14s
clippy	27s
check-ubuntu-latest	24s
build-ubuntu-latest-release	1m 2s
check-macos-latest	32s
rustfmt	11s
build-ubuntu-latest-debug	41s
check-windows-latest	2m 34s
build-macos-latest-release	1m 14s
build-macos-latest-debug	52s
build-windows-latest-release	3m 26s
build-windows-latest-debug	2m 30s
clippy-upload	15s
verify all tests pass	1s
	14m 23s

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