Support COPY_FORMATS

[joshtemple]

Copy Formats (from the Harlequin docs)

Some adapters may facilitate exporting data locally. By setting the COPY_FORMATS class variable on their subclass of HarlequinAdapter and implementing HarlequinConnection.copy(), they can enable their users to use Harlequin’s Data Exporter UI.

COPY_FORMATS is a list of HarlequinCopyFormat instances, which define a name, label, one or more file extensions associated with the format, and a list of AbstractOption subclass instances that define options for the format. For more information, see the source in the harlequin.options module, or the DuckDB implementation.