Relax constraint that UnderlyingGraph labels must impl Copy to simplify code

added 6 commits

• 192d2d93...2a6a9b46 - 4 commits from branch master
• 10e37879 - Relax constraint that UnderlyingGraph labels must impl Copy
• 82624234 - Remove useless conversions

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Jenkins job DGRPH/gitlab-builds #2661 failed in 23 min.
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added 6 commits

• 82624234...04fe2f94 - 4 commits from branch master
• 6f477b89 - Relax constraint that UnderlyingGraph labels must impl Copy
• 304bec1a - Remove useless conversions

Compare with previous version

Jenkins job DGRPH/gitlab-builds #2690 succeeded in 7 min 9 sec.
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merged