More edge cases

Toolkit.Foundation/ICache.cs

@@ -7,11 +7,13 @@ public interface ICache<TValue> :
 
     void Clear();
 
-    bool TryGetValue(TValue key, out TValue? item);
+    bool Contains(TValue key);
 
     int IndexOf(TValue value);
 
     bool Remove(TValue value);
+
+    bool TryGetValue(TValue key, out TValue? item);
 }
 
 public interface ICache<TKey, TValue> :
@@ -25,6 +27,8 @@ public interface ICache<TKey, TValue> :
 
     void Clear();
 
+    bool Contains(TKey key);
+
     int IndexOf(TKey key);
 
     bool Remove(TKey key);