Make `as_duckplyr_df` as a generic function

[eitsupi]

Ideally this function could also support something like nanoarrow_array_stream?

In the integration of the arrow and duckdb packages several years ago, the to_duckdb() function was created on the arrow package side, but looking at the Japanese R community, I saw a situation where the arrow package was also installed just to use the to_duckdb() function, even though they only wanted to use DuckDB.
To avoid such a situation, I feel that something like the as_duckplyr_df function should be created as a generic function.

[krlmlr]

Thanks, interesting. I wonder what the implementation of as_duckplyr_df.nanoarrow_array_stream() would look like?