Fix SQL macros parser handling and add coverage

[Gimyoonsoo]

/claim #71

Summary

• Normalize node-sql-parser output in the SQL macros plugin so single-statement parses and multi-statement parses are handled consistently.
• Fix the preventSelectStar guard for single SELECT * statements, which were previously allowed when astify() returned an object instead of an array.
• Add focused Vitest coverage for SQL macros plugin behavior: missing data source passthrough, external data source passthrough, non-admin SELECT * rejection, admin exception, and $_exclude(...) expansion.

Verification

• node_modules\.bin\vitest.exe run plugins\sql-macros\index.test.ts
• node_modules\.bin\prettier.exe --check plugins\sql-macros\index.ts plugins\sql-macros\index.test.ts
• git diff --check
• Attempted full node_modules\.bin\vitest.exe run; it still fails in existing src/rls/index.test.ts assertions, with this new SQL macros test file passing in that run.