feat: support system proxy (#515)

internal/protocol/http/fetcher.go

@@ -451,12 +451,11 @@ func (f *Fetcher) splitChunk() (chunks []*chunk) {
 }
 
 func (f *Fetcher) buildClient() *http.Client {
-	transport := &http.Transport{}
+	transport := &http.Transport{
+		Proxy: f.ctl.ProxyConfig.ToHandler(),
+	}
 	// Cookie handle
 	jar, _ := cookiejar.New(nil)
-	if f.ctl.ProxyUrl != nil {
-		transport.Proxy = http.ProxyURL(f.ctl.ProxyUrl)
-	}
 	return &http.Client{
 		Transport: transport,
 		Jar:       jar,