func SetHeader(vv ...string) Setter {
	return func(c *Cast) error {
		if len(vv)%2 != 0 {
			return fmt.Errorf("vv must have even params")
		}
		for i := 0; i < len(vv); i += 2 {
			c.header.Set(vv[i], vv[i+1])
		}
		return nil
	}
}
SetHeader provides an easy way to set header.
package cast
import (
	"fmt"
	"net/http"
	"time"
	"github.com/cep21/circuit/v3"
	"github.com/sirupsen/logrus"
)
type Setter func(cast *Cast) error
func WithBaseURL(url string) Setter {
	return func(c *Cast) error {
		c.baseURL = url
		return nil
	}
}
func WithHeader(h http.Header) Setter {
	return func(c *Cast) error {
		c.header = h
		return nil
	}
}