perf: optimize copy on write attributes (#74) #112

Job	Run time
test-platforms-and-versions (ubuntu-latest, 19)	2m 25s
test-platforms-and-versions (ubuntu-latest, 17)	2m 28s
test-contract-tests	2m 45s
test-platforms-and-versions (ubuntu-latest, 8)	2m 20s
test-platforms-and-versions (ubuntu-latest, 11)	2m 27s
test-packaging	3m 27s
	15m 52s

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