Cleanup.

src/ZoneTree/Collections/SkipList.cs

@@ -306,7 +306,7 @@ public class SkipListNode
         /// to properly aligned memory locations no larger than the native word size
         /// (the size of type native int) is atomic.
         /// </summary>
-        private static bool IsValueAssignmentAtomic =
+        private static readonly bool IsValueAssignmentAtomic =
             Unsafe.SizeOf<TValue>() <= IntPtr.Size;
 
         public SkipListNode[] Next;

src/ZoneTree/IZoneTreeIterator.cs

@@ -29,11 +29,6 @@ public interface IZoneTreeIterator<TKey, TValue> : IDisposable
     /// Gets the current element at the iterator's position.
     /// </summary>
     KeyValuePair<TKey, TValue> Current { get; }
-
-    /// <summary>
-    /// Returns the current disk segment associated with the iterator.
-    /// </summary>
-    IDiskSegment<TKey, TValue> DiskSegment { get; }
 
     /// <summary>
     /// Iterates to the next element.

src/ZoneTree/Segments/Disk/SparseArrayEntry.cs

@@ -2,11 +2,11 @@
 
 public class SparseArrayEntry<TKey, TValue>
 {
-    public TKey Key;
+    public readonly TKey Key;
 
-    public TValue Value;
+    public readonly TValue Value;
 
-    public int Index;
+    public readonly int Index;
 
     public SparseArrayEntry(TKey key, TValue value, int index)
     {