fix(datasync): add guards and exception safety to JsonZstdFileSource

NEW/src/JdeScoping.DataSync/Etl/Sources/JsonZstdFileSource.cs

@@ -31,6 +31,11 @@ public sealed class JsonZstdFileSource : IImportSource
     }
 
     public Task<IDataReader> ReadDataAsync(CancellationToken cancellationToken = default)
+    {
+        if (_fileStream != null)
+            throw new InvalidOperationException("ReadDataAsync has already been called. Dispose and create a new source to read again.");
+
+        try
         {
             _fileStream = new FileStream(_filePath, FileMode.Open, FileAccess.Read, FileShare.Read,
                 bufferSize: 65536, useAsync: true);
@@ -39,6 +44,18 @@ public sealed class JsonZstdFileSource : IImportSource
 
             return Task.FromResult<IDataReader>(_reader);
         }
+        catch
+        {
+            // Clean up on failure
+            _reader?.Dispose();
+            _decompressionStream?.Dispose();
+            _fileStream?.Dispose();
+            _reader = null;
+            _decompressionStream = null;
+            _fileStream = null;
+            throw;
+        }
+    }
 
     public async ValueTask DisposeAsync()
     {