fix(sub): pass numeric XMUX counts to Clash reuse-settings (#6843)

Inbound XMUX counts such as maxConnections are stored as JSON numbers, but
buildXhttpClashOpts kept only string values, so the panel default
maxConnections: 3 never reached Clash/Mihomo clients. Numeric values are now
rendered as plain integers (FormatFloat, so 1000000 does not become 1e+06) and
zero values are still dropped.

internal/sub/clash_service.go

@@ -1018,8 +1018,15 @@ func buildXhttpClashOpts(xhttp map[string]any) map[string]any {
 			{"hMaxRequestTimes", "h-max-request-times"},
 			{"hMaxReusableSecs", "h-max-reusable-secs"},
 		} {
-			if v, ok := xmux[f.src].(string); ok && v != "" {
-				reuse[f.dst] = v
+			v, ok := nonZeroShareValue(xmux[f.src])
+			if !ok {
+				continue
+			}
+			if n, isFloat := v.(float64); isFloat {
+				// JSON numbers decode as float64, and %v would render 1000000 as "1e+06".
+				reuse[f.dst] = strconv.FormatFloat(n, 'f', -1, 64)
+			} else {
+				reuse[f.dst] = fmt.Sprint(v)
 			}
 		}
 		if v, ok := nonZeroShareValue(xmux["hKeepAlivePeriod"]); ok {