fix: default to ASCENDING when sort direction is omitted in SET SORTED BY (#1205)

[mohsinsurani]

Closes #1205.

This PR fixes an issue where ALTER TABLE ... SET SORTED BY (col) preserved DuckDB's ORDER_DEFAULT sort direction in DuckLake's transaction-local sort metadata. That default could later be interpreted as descending during sorted inserts, instead of following the expected default behavior of ascending order.

Changes

• Normalize omitted sort direction to ASCENDING in src/storage/ducklake_table_entry.cpp.
• Preserve explicit DESCENDING behavior unchanged.
• Add a regression test at test/sql/sorted_table/insert_sorted_default_direction.test.

Testing

• Verified locally that insert_sorted_default_direction.test fails on HEAD before the patch.
• Verified locally that insert_sorted_default_direction.test passes after the patch.
• Verified locally that insert_sorted_basic.test still passes.

Note to Maintainers

I attempted broader debug-suite testing locally, but full execution was blocked by an existing ASAN stack-overflow failure in parser/init paths on main. The focused regression test and a related sorted insert test are green locally, and I’m relying on CI for the full verification matrix.

[Alex-Monahan]

Howdy and thank you for your help!
Would you be able to target the v1.5 variegata branch instead of main? We like having bug fixes on that branch and new features on main.

Much appreciated!

[mohsinsurani]

Done, I rebased the branch onto v1.5-variegata and force-pushed the updated PR branch. I also reran the focused regression test and insert_sorted_basic.test locally against the v1.5 base; both pass.

[pdet]

Thanks!