Added notion of lifetime to TFOperation, TFOutput and TFInput, dependent on their graph.

TensorFlowSharp/AdditionalAssemblyInfo.cs

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+using System.Runtime.CompilerServices;
+
+[assembly: InternalsVisibleTo("TensorFlowSharp.Tests.CSharp")]

TensorFlowSharp/Foundation/RangeChecks.cs

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+using System;
+using System.Runtime.CompilerServices;
+
+namespace TensorFlowSharp.Foundation
+{
+    internal static class RangeChecks
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static bool IsWithinRange(int value, int minInclusive, int maxExclusive) => minInclusive <= value && value < maxExclusive;
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static bool IsWithinRange<T>(T obj, T minInclusive, T maxExcluded)
+            where T : IComparable<T>
+        {
+            return minInclusive.CompareTo(obj) <= 0 && 0 < maxExcluded.CompareTo(obj);
+        }
+
+        public static int Assert(int value, string name, int minInclusive, int maxExclusive)
+        {
+            return IsWithinRange(value, minInclusive, maxExclusive)
+                ? value
+                : throw new ArgumentOutOfRangeException(FormattableString.Invariant($"Expected '{name}' to be within [{minInclusive}, {maxExclusive}), but was {value}"));
+        }
+    }
+}

TensorFlowSharp/Foundation/TFSharpDebug.cs

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+using System;
+using System.Runtime.CompilerServices;
+
+namespace TensorFlowSharp.Foundation
+{
+    internal delegate void DebugAction();
+    internal delegate T DebugFunc<T>();
+
+    internal static class TFSharpDebug
+    {
+        private const bool IsDebug = 
+#if DEBUG
+            true;
+#else
+            false;
+#endif
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static T AssertNotNull<T>(T obj, string name)
+            where T : class
+        {
+            return IsDebug
+                ? obj ?? throw new ArgumentNullException(name)
+                : obj;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static T AssertWithinLimits<T>(T obj, string name, T minInclusive, T maxExcluded)
+            where T : IComparable<T>
+        {
+
+            if (!IsDebug || RangeChecks.IsWithinRange(obj, minInclusive, maxExcluded))
+                return obj;
+            else
+                throw new ArgumentOutOfRangeException(FormattableString.Invariant($"Expected '{name}' to be between [{minInclusive}, {maxExcluded})"));
+        }
+    }
+}