replace v6 with experimental v7 code

src/MpvNet/ExtensionMethod/StringExtension.cs

@@ -0,0 +1,30 @@
+
+using System.Globalization;
+
+namespace MpvNet.ExtensionMethod;
+
+public static class StringExtension
+{
+    public static string ToUpperEx(this string instance) => (instance != null) ? instance.ToUpperInvariant() : "";
+
+    public static string ToLowerEx(this string instance) => (instance != null) ? instance.ToLowerInvariant() : "";
+
+    public static string TrimEx(this string? instance) => (instance == null) ? "" : instance.Trim();
+
+    public static int ToInt(this string instance, int defaultValue = 0)
+    {
+        if (int.TryParse(instance, out int result))
+            return result;
+
+        return defaultValue;
+    }
+
+    public static float ToFloat(this string instance) =>
+        float.Parse(instance.Replace(",", "."), NumberStyles.Float, CultureInfo.InvariantCulture);
+
+    public static bool ContainsEx(this string? instance, string? value) =>
+        !string.IsNullOrEmpty(instance) && !string.IsNullOrEmpty(value) && instance.Contains(value);
+
+    public static bool StartsWithEx(this string? instance, string? value) =>
+        (instance != null && value != null) && instance.StartsWith(value);
+}