Remove HostString.Port string alloc in HostString.cs (#19082)

#19064

Author: samsosa

src/Http/Http.Abstractions/src/HostString.cs

@@ -96,7 +96,7 @@ public int? Port
                 GetParts(_value, out var host, out var port);
 
                 if (!StringSegment.IsNullOrEmpty(port)
-                    && int.TryParse(port.ToString(), NumberStyles.None, CultureInfo.InvariantCulture, out var p))
+                    && int.TryParse(port.AsSpan(), NumberStyles.None, CultureInfo.InvariantCulture, out var p))
                 {
                     return p;
                 }