Use TV guide for livestreams

Jellyfin.Plugin.SRFPlay/Utilities/UrnHelper.cs

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+using System;
+using System.Security.Cryptography;
+using System.Text;
+
+namespace Jellyfin.Plugin.SRFPlay.Utilities;
+
+/// <summary>
+/// Helper class for URN-related operations.
+/// </summary>
+public static class UrnHelper
+{
+    /// <summary>
+    /// Generates a deterministic GUID from a URN.
+    /// This ensures the same URN always produces the same GUID.
+    /// MD5 is used for non-cryptographic purposes only (generating stable IDs).
+    /// </summary>
+    /// <param name="urn">The URN to convert.</param>
+    /// <returns>A deterministic GUID string.</returns>
+#pragma warning disable CA5351 // MD5 is used for non-cryptographic purposes (ID generation)
+    public static string ToGuid(string urn)
+    {
+        var hash = MD5.HashData(Encoding.UTF8.GetBytes(urn));
+        var guid = new Guid(hash);
+        return guid.ToString();
+    }
+#pragma warning restore CA5351
+}