refactor: add versioning to cf cache

Add a version number field to the custom format cache object. This is an
attempt at future-proofing the cache in case I ever need to update the
schema in a non-backward compatible way.

src/Trash.Tests/Radarr/CustomFormat/CachePersisterTest.cs

@@ -118,5 +118,36 @@ namespace Trash.Tests.Radarr.CustomFormat
             ctx.Persister.Update(new List<ProcessedCustomFormatData>());
             ctx.Persister.CfCache.Should().NotBeNull();
         }
+
+        [Test]
+        public void Accept_loaded_cache_when_versions_match()
+        {
+            var ctx = new Context();
+
+            var testCfObj = new CustomFormatCache
+            {
+                Version = CustomFormatCache.LatestVersion,
+                TrashIdMappings = new List<TrashIdMapping> {new("", "", 5)}
+            };
+            ctx.ServiceCache.Load<CustomFormatCache>().Returns(testCfObj);
+            ctx.Persister.Load();
+            ctx.Persister.CfCache.Should().NotBeNull();
+        }
+
+        [TestCase(CustomFormatCache.LatestVersion-1)]
+        [TestCase(CustomFormatCache.LatestVersion+1)]
+        public void Set_loaded_cache_to_null_if_versions_mismatch(int versionToTest)
+        {
+            var ctx = new Context();
+
+            var testCfObj = new CustomFormatCache
+            {
+                Version = versionToTest,
+                TrashIdMappings = new List<TrashIdMapping> {new("", "", 5)}
+            };
+            ctx.ServiceCache.Load<CustomFormatCache>().Returns(testCfObj);
+            ctx.Persister.Load();
+            ctx.Persister.CfCache.Should().BeNull();
+        }
     }
 }

src/Trash/Radarr/CustomFormat/CachePersister.cs

@@ -27,6 +27,15 @@ namespace Trash.Radarr.CustomFormat
             if (CfCache != null)
             {
                 Log.Debug("Loaded Cache");
+
+                // If the version is higher OR lower, we invalidate the cache. It means there's an
+                // incompatibility that we do not support.
+                if (CfCache.Version != CustomFormatCache.LatestVersion)
+                {
+                    Log.Information("Cache version mismatch ({OldVersion} vs {LatestVersion}); ignoring cache data",
+                        CfCache.Version, CustomFormatCache.LatestVersion);
+                    CfCache = null;
+                }
             }
             else
             {

src/Trash/Radarr/CustomFormat/Models/Cache/CustomFormatCache.cs

@@ -6,6 +6,9 @@ namespace Trash.Radarr.CustomFormat.Models.Cache
     [CacheObjectName("custom-format-cache")]
     public class CustomFormatCache
     {
+        public const int LatestVersion = 1;
+
+        public int Version { get; init; } = LatestVersion;
         public List<TrashIdMapping> TrashIdMappings { get; init; } = new();
     }