test: cover sql macros plugin

[wangxiangzhu88-droid]

/claim #71

Summary

• Add focused coverage for the SQL macros plugin's no-data-source, internal $_exclude(...), external data source, non-admin SELECT *, and admin SELECT * paths.
• Fix checkSelectStar to handle parser results returned as either a single AST object or an array, so preventSelectStar rejects single-statement SELECT * queries as intended.

Tests

• vitest run plugins/sql-macros/index.test.ts
• prettier --check plugins/sql-macros/index.ts plugins/sql-macros/index.test.ts
• vitest run currently reports existing failures in src/rls/index.test.ts unrelated to this change; the new SQL macros tests pass.