Replace the remaining `pylance` (`take_blobs`) snippet in the LeRobot
integration guide with `Table.fetch_blob_files`, document how to open
`.lance` datasets directly with `lancedb` alongside a
`pylance`-to-`lancedb` call mapping on `/basics/lance`, and clarify in
installation docs that the optional `pylance` extra is only needed for
engine/connector authors or format-level fragment APIs.