ethclient/simulated: implement new sim backend (#28202)

This is a rewrite of the 'simulated backend', an implementation of the ethclient interfaces
which is backed by a simulated blockchain. It was getting annoying to maintain the old
version of the simulated backend feature because there was a lot of code duplication with
the main client. 

The new version is built using parts that we already have: an in-memory geth node instance
running in developer mode provides the chain, while the Go API is provided by ethclient.
A backwards-compatibility wrapper is provided, but the simulated backend has also moved to
a more sensible import path: github.com/ethereum/go-ethereum/ethclient/simulated

---------

Co-authored-by: Felix Lange <[email protected]>
Co-authored-by: Gary Rong <[email protected]>

accounts/abi/bind/backend.go

@@ -84,6 +84,11 @@ type BlockHashContractCaller interface {
 // used when the user does not provide some needed values, but rather leaves it up
 // to the transactor to decide.
 type ContractTransactor interface {
+	ethereum.GasEstimator
+	ethereum.GasPricer
+	ethereum.GasPricer1559
+	ethereum.TransactionSender
+
 	// HeaderByNumber returns a block header from the current canonical chain. If
 	// number is nil, the latest known header is returned.
 	HeaderByNumber(ctx context.Context, number *big.Int) (*types.Header, error)
@@ -93,38 +98,6 @@ type ContractTransactor interface {
 
 	// PendingNonceAt retrieves the current pending nonce associated with an account.
 	PendingNonceAt(ctx context.Context, account common.Address) (uint64, error)
-
-	// SuggestGasPrice retrieves the currently suggested gas price to allow a timely
-	// execution of a transaction.
-	SuggestGasPrice(ctx context.Context) (*big.Int, error)
-
-	// SuggestGasTipCap retrieves the currently suggested 1559 priority fee to allow
-	// a timely execution of a transaction.
-	SuggestGasTipCap(ctx context.Context) (*big.Int, error)
-
-	// EstimateGas tries to estimate the gas needed to execute a specific
-	// transaction based on the current pending state of the backend blockchain.
-	// There is no guarantee that this is the 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.
-	EstimateGas(ctx context.Context, call ethereum.CallMsg) (gas uint64, err error)
-
-	// SendTransaction injects the transaction into the pending pool for execution.
-	SendTransaction(ctx context.Context, tx *types.Transaction) error
-}
-
-// ContractFilterer defines the methods needed to access log events using one-off
-// queries or continuous event subscriptions.
-type ContractFilterer interface {
-	// FilterLogs executes a log filter operation, blocking during execution and
-	// returning all the results in one batch.
-	//
-	// TODO(karalabe): Deprecate when the subscription one can return past data too.
-	FilterLogs(ctx context.Context, query ethereum.FilterQuery) ([]types.Log, error)
-
-	// SubscribeFilterLogs creates a background log filtering operation, returning
-	// a subscription immediately, which can be used to stream the found events.
-	SubscribeFilterLogs(ctx context.Context, query ethereum.FilterQuery, ch chan<- types.Log) (ethereum.Subscription, error)
 }
 
 // DeployBackend wraps the operations needed by WaitMined and WaitDeployed.
@@ -133,6 +106,12 @@ type DeployBackend interface {
 	CodeAt(ctx context.Context, account common.Address, blockNumber *big.Int) ([]byte, error)
 }
 
+// ContractFilterer defines the methods needed to access log events using one-off
+// queries or continuous event subscriptions.
+type ContractFilterer interface {
+	ethereum.LogFilterer
+}
+
 // ContractBackend defines the methods needed to work with contracts on a read-write basis.
 type ContractBackend interface {
 	ContractCaller