Initial port of cache functions from java client

src/KubernetesClient/KubernetesClient.csproj

@@ -45,4 +45,8 @@
     <PackageReference Include="IdentityModel.OidcClient" Version="3.1.2" />
   </ItemGroup>
 
+  <ItemGroup>
+    <Folder Include="Util\Informer" />
+  </ItemGroup>
+
 </Project>

src/KubernetesClient/Util/Common/CallGeneratorParams.cs

@@ -0,0 +1,16 @@
+namespace k8s.Util.Common
+{
+    public class CallGeneratorParams
+    {
+        public bool Watch { get; }
+        public string ResourceVersion { get; }
+        public int? TimeoutSeconds { get; }
+
+        public CallGeneratorParams(bool watch, string resourceVersion, int? timeoutSeconds)
+        {
+            Watch = watch;
+            ResourceVersion = resourceVersion;
+            TimeoutSeconds = timeoutSeconds;
+        }
+    }
+}

src/KubernetesClient/Util/Common/CollectionsExtensions.cs

@@ -0,0 +1,43 @@
+using System;
+using System.Collections.Generic;
+
+namespace k8s.Util.Common
+{
+    internal static class CollectionsExtensions
+    {
+        public static void AddRange<T>(this HashSet<T> hashSet, ICollection<T> items)
+        {
+            if (items == null)
+            {
+                return;
+            }
+
+            foreach (var item in items)
+            {
+                hashSet?.Add(item);
+            }
+        }
+
+        internal static TValue ComputeIfAbsent<TKey, TValue>(this IDictionary<TKey, TValue> dictionary, TKey key, Func<TKey, TValue> mappingFunction)
+        {
+            if (dictionary is null)
+            {
+                throw new ArgumentNullException(nameof(dictionary));
+            }
+
+            if (dictionary.TryGetValue(key, out var value))
+            {
+                return value;
+            }
+
+            if (mappingFunction == null)
+            {
+                throw new ArgumentNullException(nameof(mappingFunction));
+            }
+
+            var newKey = mappingFunction(key);
+            dictionary[key] = newKey;
+            return newKey;
+        }
+    }
+}