feat(server/v2): add SimulateWithState to AppManager

There is already the QueryWithState method to query against a modified
state, but the Simulate analog was missing.

This is useful in particular when a server component receives different
transactions at different times, and wants to ensure that subsequent
transactions would be valid to apply after the prior transactions.

In other words, the first received transaction can be validated with
Simulate; then the returned corestore.WriterMap is used to seed the
input to the following call to SimulateWithState; and then the returned
corestore.WriterMap is used for all following SimulateWithState calls.

While it is currently impossible for SimulateWithState to return an
error, an error value is  in the return signature for symmetry with
other AppManager methods and to allow the possibility of returned errors
in the future.

There were no existing tests in the server/v2/appmanager package, to be
expanded to include test coverage for the new method.

server/v2/appmanager/appmanager.go

@@ -41,6 +41,10 @@ type AppManager[T transaction.Tx] interface {
 	// Simulate runs validation and execution flow of a Tx.
 	Simulate(ctx context.Context, tx T) (server.TxResult, corestore.WriterMap, error)
 
+	// SimulateWithState runs validation and execution flow of a Tx,
+	// using the provided state instead of loading the latest state from the underlying database.
+	SimulateWithState(ctx context.Context, state corestore.ReaderMap, tx T) (server.TxResult, corestore.WriterMap, error)
+
 	// Query queries the application at the provided version.
 	// CONTRACT: Version must always be provided, if 0, get latest
 	Query(ctx context.Context, version uint64, request transaction.Msg) (transaction.Msg, error)
@@ -193,6 +197,13 @@ func (a appManager[T]) Simulate(ctx context.Context, tx T) (server.TxResult, cor
 	return result, cs, nil
 }
 
+// SimulateWithState runs validation and execution flow of a Tx,
+// using the provided state instead of loading the latest state from the underlying database.
+func (a appManager[T]) SimulateWithState(ctx context.Context, state corestore.ReaderMap, tx T) (server.TxResult, corestore.WriterMap, error) {
+	result, cs := a.stf.Simulate(ctx, state, a.config.SimulationGasLimit, tx) // TODO: check if this is done in the antehandler
+	return result, cs, nil
+}
+
 // Query queries the application at the provided version.
 // CONTRACT: Version must always be provided, if 0, get latest
 func (a appManager[T]) Query(ctx context.Context, version uint64, request transaction.Msg) (transaction.Msg, error) {