refactor: move abis to system_init

* closes #31

internal/tasker/task/system.go

@@ -147,12 +147,7 @@ func GiftTokenProcessor(
 			return err
 		}
 
-		abi, err := w3.NewFunc("mint(address,uint256)", "")
-		if err != nil {
-			return err
-		}
-
-		input, err := abi.EncodeArgs(publicKey, system.GiftableTokenValue)
+		input, err := system.Abis["mint"].EncodeArgs(publicKey, system.GiftableTokenValue)
 		if err != nil {
 			return fmt.Errorf("ABI encode failed %v: %w", err, asynq.SkipRetry)
 		}

internal/tasker/task/transfer.go

@@ -55,12 +55,7 @@ func TransferToken(
 			return err
 		}
 
-		abi, err := w3.NewFunc("transfer(address,uint256)", "bool")
-		if err != nil {
-			return err
-		}
-
-		input, err := abi.EncodeArgs(w3.A(p.To), parseTransferValue(p.Amount, system.TokenDecimals))
+		input, err := system.Abis["transfer"].EncodeArgs(w3.A(p.To), parseTransferValue(p.Amount, system.TokenDecimals))
 		if err != nil {
 			return fmt.Errorf("ABI encode failed %v: %w", err, asynq.SkipRetry)
 		}

internal/tasker/types.go

@@ -7,6 +7,7 @@ import (
 	"time"
 
 	"github.com/celo-org/celo-blockchain/common"
+	"github.com/grassrootseconomics/w3-celo-patch"
 )
 
 type (
@@ -15,6 +16,7 @@ type (
 )
 
 type SystemContainer struct {
+	Abis                  map[string]*w3.Func
 	GasRefillThreshold    *big.Int
 	GasRefillValue        *big.Int
 	GiftableGasValue      *big.Int