crypto/bn256: switch to gnark again (#32659)

We recently update our default implementation to gnark in
#32024
Then we found a consensus issue and reverted it in
65d77c5
We fixed the consensus issue and have been fuzzing it more since then in
https://github.com/ethereum/go-ethereum/pull/32055/files
#32065
https://github.com/ethereum/go-ethereum/pull/32055/files

So I think now is the time to update it back to gnark

Author: MariusVanDerWijden

crypto/bn256/bn256_fast.go

@@ -9,18 +9,18 @@
 package bn256
 
 import (
-	bn256cf "github.com/ethereum/go-ethereum/crypto/bn256/cloudflare"
+	gnark "github.com/ethereum/go-ethereum/crypto/bn256/gnark"
 )
 
 // G1 is an abstract cyclic group. The zero value is suitable for use as the
 // output of an operation, but cannot be used as an input.
-type G1 = bn256cf.G1
+type G1 = gnark.G1
 
 // G2 is an abstract cyclic group. The zero value is suitable for use as the
 // output of an operation, but cannot be used as an input.
-type G2 = bn256cf.G2
+type G2 = gnark.G2
 
 // PairingCheck calculates the Optimal Ate pairing for a set of points.
 func PairingCheck(a []*G1, b []*G2) bool {
-	return bn256cf.PairingCheck(a, b)
+	return gnark.PairingCheck(a, b)
 }