[goransh-walia]

Fixes #205

What problem does this PR solve?

Issue link: #205

Columns output by USING were previously determined by JoinType, causing incorrect expression evaluation and column hiding behavior in joins.

What is changed and how it works?

• Modified UsingColumn::expr() in src/binder/mod.rs to always generate a ScalarExpression::Coalesce containing both left and right column expressions typed with LogicalType::max_logical_type, rather than selecting expressions based on JoinType.
• Modified UsingColumn::hides_column() to always hide right_column instead of choosing between left_column and right_column based on whether the join was a right outer join.
• Renamed join_type to _join_type in UsingColumn.

Code changes

• Has Rust code change
• Has CI related scripts change

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Note for reviewer

The full test suite was not run locally, so I'm relying on CI to confirm.

AI-assisted.

[KKould]

Thank you for your contribution; you can try running make test-all to test it locally.