Add mcl backend #242

Job	Run time
kzg_ci	37s
backend_ci (ubuntu-latest, blst)	14m 53s
backend_ci (ubuntu-latest, zkcrypto)	31m 37s
backend_ci (ubuntu-latest, arkworks5)	18m 25s
backend_ci (ubuntu-latest, arkworks4)	19m 54s
backend_ci (ubuntu-latest, arkworks3)	17m 34s
backend_ci (ubuntu-latest, constantine)	26m 10s
backend_ci (ubuntu-latest, mcl)	15m 45s
backend_ci (windows-latest, blst)	5m 59s
backend_ci (windows-latest, zkcrypto)	9m 4s
backend_ci (windows-latest, arkworks5)	6m 24s
backend_ci (windows-latest, arkworks4)	6m 47s
backend_ci (windows-latest, arkworks3)	6m 54s
backend_ci (windows-latest, constantine)	10m 17s
backend_ci (macos-latest, blst)	5m 53s
backend_ci (macos-latest, zkcrypto)	8m 0s
backend_ci (macos-latest, arkworks5)	6m 39s
backend_ci (macos-latest, arkworks4)	7m 17s
backend_ci (macos-latest, arkworks3)	6m 32s
backend_ci (macos-latest, constantine)	12m 9s
backend_ci (macos-latest, mcl)	6m 35s
	4h 3m 25s

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