optimize the first operator in a frozen-sequence to improve performance by reducing overhead in item access

Author: fembina

Sources/Falko.Common.Sequences/Sequences/FrozenSequence.Operator.First.cs

@@ -18,15 +18,23 @@ public T First()
 
     public T First(Func<T, bool> predicate)
     {
+        var itemsCount = _itemsCount;
+
+        if (itemsCount is 0) SequenceExceptions.ThrowIfEmpty(itemsCount);
+
         ArgumentNullException.ThrowIfNull(predicate);
 
-        foreach (ref readonly var item in AsSpan())
+        scoped ref var itemsReference = ref MemoryMarshal.GetArrayDataReference(_items);
+
+        for (var itemIndex = 0; itemIndex < itemsCount; itemIndex++)
         {
+            var item = Unsafe.Add(ref itemsReference, itemIndex);
+
             if (predicate(item)) return item;
         }
 
         SequenceExceptions.ThrowNotMatchAny();
-        return default!; // This line is unreachable
+        return default; // This line is unreachable
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]