[DuckDB] Support export table from DuckDB to lance

Problem Statement

Duckdb allows to export a table via COPY/EXPORT command.

https://duckdb.org/docs/sql/statements/export.html

-- export the table contents with the given options
EXPORT DATABASE 'target_directory' (FORMAT CSV, DELIMITER '|');
-- export the table contents as parquet
EXPORT DATABASE 'target_directory' (FORMAT PARQUET);

Desired Behavior

In Lance duckdb extension, we could support COPY statement

COPY (SELECT * FROM tbl) TO 'output.lance' (FORMAT LANCE);

Start by locating the Lance DuckDB extension and its COPY statement integration points. Read the linked DuckDB export documentation and trace how existing table-export formats are handled. Done means the extension accepts COPY (SELECT * FROM tbl) TO 'output.lance' (FORMAT LANCE) and exports the selected table to a Lance file.