feat(metrics/family): add `Family::get_or_create_clone()` #13

Job	Run time
Check rustdoc intra-doc links	37s
Check	1m 40s
Cross compile (armv7-unknown-linux-gnueabihf)	11s
Clippy	1m 13s
Cross compile (powerpc-unknown-linux-gnu)	16s
Cross compile (powerpc64-unknown-linux-gnu)	20s
Rustfmt	21s
Cross compile (wasm32-unknown-unknown)	11s
Test Suite	1m 38s
	6m 27s

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