DuckDB reads Lance tables out of a table bucket over S3 with no catalog
involved, which is the property that keeps the data readable by anything
that does not speak the namespace protocol.
Records the one place the layout costs us: DuckDB's replacement scan
recognises a dataset by a .lance path suffix, which tables created through
this catalog deliberately do not have, so __lance_scan is the way in. Also
notes that the documented ATTACH ... (TYPE lance) form fails in 1.5.5.
Chris Lu