C# Re-implementation (#5)

Re-implementation of C# interceptors SDK with clearer focus on
server-side / gateway interceptors.
Fixes a lot of issues with the existing implementation.
Still more boilerplate than I'm happy with, but this is better than what
was there. Will refine further in later PRs.

csharp/sdk/samples/AvatarMoodInterceptorSample/AvatarState.cs

@@ -0,0 +1,36 @@
+namespace AvatarMoodInterceptorSample;
+
+public enum Mood
+{
+    Neutral,
+    Happy,
+    Curious,
+    Focused,
+    Confused,
+    Frustrated,
+}
+
+public sealed class AvatarState
+{
+    private readonly object _lock = new();
+    private readonly List<Mood> _history = [];
+
+    public Mood Current { get; private set; } = Mood.Neutral;
+    public float Confidence { get; private set; }
+    public string? ClassifierModel { get; private set; }
+    public IReadOnlyList<Mood> History
+    {
+        get { lock (_lock) { return _history.ToArray(); } }
+    }
+
+    public void Update(Mood mood, float confidence, string? classifierModel)
+    {
+        lock (_lock)
+        {
+            Current = mood;
+            Confidence = confidence;
+            ClassifierModel = classifierModel;
+            _history.Add(mood);
+        }
+    }
+}