Add zki.ISAccFeeOut generation for circuits compat

- add IntermediateStates AccFeeOut correct generation for circuits
compatibility at ZKInputs
- Fix formatAccumulatedFees
- organize ZKInputs tests to check compatibility with Circom circuits
- Add TestZKInputs2
    - which checks ZKInputs for 4 L1 txs + 2 L2Txs with fees
    - tested with Hermez Circom circuits

db/statedb/utils.go

@@ -170,7 +170,7 @@ func formatAccumulatedFees(collectedFees map[common.TokenID]*big.Int, orderToken
 	for i := 0; i < len(orderTokenIDs); i++ {
 		tokenID := common.TokenIDFromBigInt(orderTokenIDs[i])
 		if _, ok := collectedFees[tokenID]; ok {
-			accFeeOut[i] = collectedFees[tokenID]
+			accFeeOut[i] = new(big.Int).Set(collectedFees[tokenID])
 		} else {
 			accFeeOut[i] = big.NewInt(0)
 		}