"improving" pair handler clean up and some other stuff

LightlessSync/FileCache/FileCacheManager.cs

@@ -280,6 +280,26 @@ public sealed class FileCacheManager : IHostedService
         return CreateFileEntity(cacheFolder, CachePrefix, fi);
     }
 
+    public FileCacheEntity? CreateCacheEntryWithKnownHash(string path, string hash)
+    {
+        if (string.IsNullOrWhiteSpace(hash))
+        {
+            return CreateCacheEntry(path);
+        }
+
+        FileInfo fi = new(path);
+        if (!fi.Exists) return null;
+        _logger.LogTrace("Creating cache entry for {path} using provided hash", path);
+        var cacheFolder = _configService.Current.CacheFolder;
+        if (string.IsNullOrEmpty(cacheFolder)) return null;
+        if (!TryBuildPrefixedPath(fi.FullName, cacheFolder, CachePrefix, out var prefixedPath, out _))
+        {
+            return null;
+        }
+
+        return CreateFileCacheEntity(fi, prefixedPath, hash);
+    }
+
     public FileCacheEntity? CreateFileEntry(string path)
     {
         FileInfo fi = new(path);