Supports downloading and generating future universe files

[Romazes]

Expected Behavior

LEAN should provide a generic data downloader wrapper that:

• Supports downloading historical market data from multiple data sources via their respective historical providers
• Supports downloading universe files (Future)

Actual Behavior

Each data source currently implements its own DataDownloader with:

• Duplicated logic for request handling, retries, pagination, file output, and error handling
  For example, PolygonDataDownloader explicitly implements this logic instead of reusing a shared abstraction:
  https://github.com/QuantConnect/Lean.DataSource.Polygon/blob/master/QuantConnect.Polygon/PolygonDataDownloader.cs

Potential Solution

Introduce a Generic DataDownloader wrapper / base implementation that:

• Encapsulates shared downloader logic

Example for Brokerages: https://github.com/QuantConnect/Lean/blob/master/DownloaderDataProvider/Models/BrokerageDataDownloader.cs

Checklist

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