all: switch gas limits from big.Int to uint64

interfaces.go

@@ -115,7 +115,7 @@ type ChainSyncReader interface {
 type CallMsg struct {
 	From     common.Address  // the sender of the 'transaction'
 	To       *common.Address // the destination contract (nil for contract creation)
-	Gas      *big.Int        // if nil, the call executes with near-infinite gas
+	Gas      uint64          // if 0, the call executes with near-infinite gas
 	GasPrice *big.Int        // wei <-> gas exchange ratio
 	Value    *big.Int        // amount of wei sent along with the call
 	Data     []byte          // input data, usually an ABI-encoded contract method invocation
@@ -200,7 +200,7 @@ type PendingContractCaller interface {
 // true gas limit requirement as other transactions may be added or removed by miners, but
 // it should provide a basis for setting a reasonable default.
 type GasEstimator interface {
-	EstimateGas(ctx context.Context, call CallMsg) (usedGas *big.Int, err error)
+	EstimateGas(ctx context.Context, call CallMsg) (uint64, error)
 }
 
 // A PendingStateEventer provides access to real time notifications about changes to the