Implement diff-reporter PoC (#5)

src/Recordingtest.DiffReporter/DiffModels.cs

@@ -0,0 +1,11 @@
+namespace Recordingtest.DiffReporter;
+
+public sealed record DiffSummary(int Added, int Removed, int Changed);
+
+public sealed record Hunk(int LineOrOffset, string Kind, string Before, string After);
+
+public sealed record DiffResult(
+    string File,
+    bool Identical,
+    IReadOnlyList<Hunk> Hunks,
+    DiffSummary Summary);