http: disable HTTP/2 to enable parallel connections

This fixes the mount read throughput issue where HTTP GET requests to the
same volume server were being serialized even with high -concurrentReaders.

The issue was that:
1. HTTP/2 multiplexes all requests over a single TCP connection
2. Even with HTTP/1.1, ForceAttemptHTTP2 defaults to true in Go

Changes:
- Set ForceAttemptHTTP2: false on http.Transport to disable HTTP/2
- Set MaxConnsPerHost: 0 (unlimited) to allow parallel connections per host
- For HTTPS, set NextProtos to only 'http/1.1' to prevent HTTP/2 negotiation

This allows multiple goroutines to use separate TCP connections to the same
volume server, enabling true parallel chunk fetching and better network
bandwidth utilization.

Relates to: #7504

weed/util/http/client/http_client.go

@@ -119,6 +119,7 @@ func NewHttpClient(clientName ClientName, opts ...HttpClientOpt) (*HTTPClient, e
 				Certificates:       []tls.Certificate{},
 				RootCAs:            caCertPool,
 				InsecureSkipVerify: false,
+				NextProtos:         []string{"http/1.1"}, // Disable HTTP/2 for parallel connections
 			}
 
 			if clientCertPair != nil {
@@ -130,6 +131,8 @@ func NewHttpClient(clientName ClientName, opts ...HttpClientOpt) (*HTTPClient, e
 	httpClient.Transport = &http.Transport{
 		MaxIdleConns:        1024,
 		MaxIdleConnsPerHost: 1024,
+		MaxConnsPerHost:     0, // 0 means no limit, allows parallel connections
+		ForceAttemptHTTP2:   false,
 		TLSClientConfig:     tlsConfig,
 	}
 	httpClient.Client = &http.Client{