fix(cubesql): preserve literal ORDER BY aliases

[jwils]

Check List

• Tests have been run in packages where changes have been made if available
• Linter has been run for changed code
• Tests for the changes have been added if not covered yet
• Docs have been added / updated if required

Description of Changes Made

CubeSQL sort pushdown can replace an aliased grouped integer literal with the literal itself. Databases that interpret integers in ORDER BY as positional ordinals can then reject the generated SQL when the ordinal exceeds the select-list width.

• Restore the generated group alias when an ORDER BY expression exactly matches a grouped literal
• Preserve sort direction, null ordering, ordinary column sorts, and existing window-expression alias handling
• Add a regression test with two literal sort keys that fails against master with a raw ORDER BY 19

Risk Assessment

Low. The rewrite is limited to ORDER BY expressions that exactly match literal expressions in the same grouped select; all other sort expressions retain their existing behavior.

Validation

• cargo test -p cubesql --lib: 776 passed, 6 ignored
• cargo clippy -p cubesql --lib --tests
• cargo fmt --all -- --check