Add `{Array,Group}::to_v3()` #796

Job	Run time
build_and_test_windows	3m 33s
clippy	34s
build_and_test_macos (macos-13)	2m 22s
build_and_test (stable, --features "")	1m 51s
codecov	1m 50s
fmt	18s
build_and_test (stable, --all-features)	2m 5s
build_and_test (stable, --no-default-features)	1m 6s
build_and_test_macos (macos-latest)	1m 22s
build_and_test (1.77, --features "")	1m 41s
minimal-versions	37s
semver	1m 44s
build_and_test (1.77, --all-features)	2m 16s
build_and_test (1.77, --no-default-features)	1m 3s
build_and_test (beta, --features "")	1m 37s
build_and_test (beta, --all-features)	2m 12s
build_and_test (beta, --no-default-features)	1m 5s
build_and_test (nightly, --features "")	1m 16s
build_and_test (nightly, --all-features)	1m 40s
build_and_test (nightly, --no-default-features)	53s
	31m 5s

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