DuckDB star and COLUMNS(...) expression macros for Ecto SQL generation.

These helpers wrap QuackDB.SQL.star/1, QuackDB.SQL.columns/1,2, and QuackDB.SQL.unpack_columns/1,2 in Ecto fragments.

DuckDB star expressions can expand one Ecto expression into multiple SQL result columns. That is useful for SQL generation and raw Repo.query!/2 execution, but it can surprise Ecto's normal result loader in Repo.all/2 select lists. Prefer these macros in predicates or when you intentionally pass generated SQL to Repo.query!/2.