Constantine backend #62

Job	Run time
benchmarks (ubuntu-latest, blst)	45m 6s
benchmarks (ubuntu-latest, zkcrypto)	57s
benchmarks (ubuntu-latest, arkworks)	54m 1s
benchmarks (ubuntu-latest, constantine)	57m 56s
benchmarks (windows-latest, blst)	36m 39s
benchmarks (windows-latest, zkcrypto)	2m 13s
benchmarks (windows-latest, arkworks)	45m 18s
benchmarks (windows-latest, constantine)	53m 39s
benchmarks (macos-11, blst)	45m 34s
benchmarks (macos-11, zkcrypto)	2m 52s
benchmarks (macos-11, arkworks)	56m 39s
benchmarks (macos-11, constantine)	1h 19m 10s
	8h 0m 4s

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