Temp commit to record attempts. Stream APIs are implemented and working. Added some new test cases based on deployed Kavita server testing.

API/Extensions/EnumerableExtensions.cs

@@ -0,0 +1,21 @@
+using System;
+using System.Collections.Generic;
+
+namespace API.Extensions
+{
+    public static class EnumerableExtensions
+    {
+        public static IEnumerable<TSource> DistinctBy<TSource, TKey>
+            (this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
+        {
+            var seenKeys = new HashSet<TKey>();
+            foreach (var element in source)
+            {
+                if (seenKeys.Add(keySelector(element)))
+                {
+                    yield return element;
+                }
+            }
+        }
+    }
+}