DuckDB: use provided schema in query_arrow to avoid schema mismatches

[sgrebnov]

Summary

Update the query_arrow method in DuckDbConnection to use the provided projected_schema parameter instead of always fetching the schema manually from DuckDB.

This makes query logic more robust by using exact target schema and avoids schema mismatch errors.

Benefits

• Prevents schema mismatches: Uses exact expected schema instead of inferred schema
• Performance improvement: Eliminates unnecessary LIMIT 0 schema discovery query and avoids additional schema casts