Added logic to stop duplicate shows from being announced using redis cache

AnimeAnnouncer/Program.cs

@@ -1,4 +1,5 @@
 using System.ComponentModel;
+using System.Security.Cryptography;
 using AnimeAnnouncer.Cache;
 using AnimeAnnouncer.RSS;
 using Mastonet;
@@ -166,7 +167,16 @@ namespace AnimeAnnouncer
                 return;
             }
 
-            // Announce
+            // Announce if unique
+            if(await tmdbCache.KeyExists($"ShowAnnounced-{supposedShowId}"))
+            {
+                Console.WriteLine($"{title} has been previously announced, so avoiding announcing it again.");
+                return;
+            }
+            else
+            {
+                _ = tmdbCache.SetPair($"ShowAnnounced-{supposedShowId}", "1");
+            }
             if(mastodonClient != null)
             {
                 try