Optimize the binary search by using unsafe

The jit was not able to tell that bounds checks could be elided.

Added an extra whistle for value types to allow for inlined comparisons.

PersistentMap/KeyStrategies/ComparableStrategy.cs

@@ -0,0 +1,17 @@
+namespace PersistentMap;
+
+using System.Runtime.CompilerServices;
+
+// This is a comparable strategy that may squeeze some extra time out of value types
+
+public readonly struct ComparableStrategy<K> : IKeyStrategy<K> where K : IComparable<K>
+{
+    public bool UsesPrefixes => false;
+    public bool UseBinarySearch => true;
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public long GetPrefix(K key) => 0;
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public int Compare(K x, K y) => x.CompareTo(y);
+}