eth/backend.go
func (b *backendInstance) PendingNonceAt(ctx context.Context, account common.Address) (uint64, error) {
	ctx, cancel := b.addTimeout(ctx)
	defer cancel()
	return b.conn.ethClient().PendingNonceAt(ctx, account)
}
func (b *backendInstance) PendingNonceAt(ctx context.Context, account common.Address) (uint64, error) {
	ctx, cancel := b.addTimeout(ctx)
	defer cancel()
	return b.conn.ethClient().PendingNonceAt(ctx, account)
}
// PendingNonceAt returns the account nonce of the given account in the pending state.
// This is the nonce that should be used for the next transaction.