cargo

Move core metrics registration into a new metriken-core crate #367

Job	Run time
audit	15s
build-ubuntu-latest-release	30s
clippy	28s
build-ubuntu-latest-debug	24s
check-ubuntu-latest	16s
build-macos-latest-release	42s
check-macos-latest	33s
rustfmt	7s
build-macos-latest-debug	43s
check-windows-latest	2m 23s
build-windows-latest-release	26s
build-windows-latest-debug	22s
clippy-upload	14s
verify all tests pass	0s
	7m 23s

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