Avoid unnecessary copies for TableChunk -> PackedData

[rjzamora]

Motivated by this comment from @wence-

Example: In cudf-polars, we convert TableChunk objects to PackedData to insert said data into an AllGather. Since there is no PackedData.from_table_chunk (nor TableChunk.to_packed_data) API, we currently call PackedData.from_cudf_packed_columns((pack(chunk.table_view(), ...), ...). This makes unnecessary copies when the underlying data is already in packed form.

Feature Request: Add a PackedData.from_table_chunk or TableChunk.to_packed_data API to take care of this conversion.