fix: implement IStore.OnNewSnapshot event in RpcStore

The RpcStore class was missing implementation of the OnNewSnapshot event
required by the IStore interface. This change adds the event declaration
and invokes it in the GetSnapshot method to maintain interface compatibility.

Author: Jim8y

src/Neo.SmartContract.Testing/Storage/Rpc/RpcStore.cs

@@ -28,6 +28,11 @@ public class RpcStore : IStore
 {
     private int _id = 0;
 
+    /// <summary>
+    /// Event raised when a new snapshot is created
+    /// </summary>
+    public event IStore.OnNewSnapshotDelegate? OnNewSnapshot;
+
     /// <summary>
     /// Url
     /// </summary>
@@ -50,7 +55,12 @@ public RpcStore(string url) : this(new Uri(url)) { }
 
     public void Delete(byte[] key) => throw new NotImplementedException();
     public void Put(byte[] key, byte[] value) => throw new NotImplementedException();
-    public IStoreSnapshot GetSnapshot() => new RpcSnapshot(this);
+    public IStoreSnapshot GetSnapshot()
+    {
+        var snapshot = new RpcSnapshot(this);
+        OnNewSnapshot?.Invoke(this, snapshot);
+        return snapshot;
+    }
     public bool Contains(byte[] key) => TryGet(key) != null;
     public void Dispose() { }