Support Narwhals DataFrames including DuckDB relation and Dask.

[MarcSkovMadsen]

In panel-extensions/panel-graphic-walker#22 I will add more support for more data sources to panel-graphic-walker. I add general DataFrame support via Narwhals because its what we are going to do for param, panel and rest of HoloViz ecosystem I believe.

With the PR above we will end up supporting

It would be very nice with

• DuckDB Relation and Dask support in pygwalker.
• General support for any Narwhals DataFrame type
• The pygwalker database Connector being a support Narwhals DataFrame type. Context.

[MarcSkovMadsen]

For now I will try to figure out how I can convert a duckdb relation to the pygwalker database connector because that is what is important for my own use cases. I've asked how in duckdb/duckdb#14768.