Support CHANGE/MODIFY COLUMN options

[KKould]

Summary

• support NULL, NOT NULL, and DEFAULT options for ALTER TABLE CHANGE/MODIFY COLUMN
• keep unsupported ALTER TABLE forms covered by SLT without adding constraint support
• simplify DDL table batch helpers by removing the redundant tuple length argument

Scope

• does not implement ADD CONSTRAINT / DROP CONSTRAINT
• does not implement CHANGE/MODIFY COLUMN ... UNIQUE

Tests

• cargo check
• cargo run -p sqllogictest-test -- --path tests/slt/alter_table.slt
• cargo run -p sqllogictest-test -- --path tests/slt/change_column.slt