test: cover sql macros plugin

[Treasure520520]

/claim #71

Summary

• add focused Vitest coverage for the SQL macros plugin
• cover no-data-source passthrough, non-internal/pragma passthrough, non-admin SELECT * blocking, admin/disabled bypasses, $_exclude(...) expansion, multiple excluded columns, and parse-error fallback
• fix two covered edge cases: node-sql-parser may return a single AST object instead of an array, and $_exclude(...) comparisons should handle excluded column names case-insensitively

Verification

• COREPACK_ENABLE_PROJECT_SPEC=0 corepack pnpm exec prettier --check plugins/sql-macros/index.ts plugins/sql-macros/index.test.ts
• COREPACK_ENABLE_PROJECT_SPEC=0 corepack pnpm vitest plugins/sql-macros/index.test.ts --run
• git diff --check
• COREPACK_ENABLE_PROJECT_SPEC=0 corepack pnpm exec tsc --noEmit --pretty false still reports existing repository errors in plugins/cdc, src/cache, src/do, and src/operation; no errors mention plugins/sql-macros
• COREPACK_ENABLE_PROJECT_SPEC=0 corepack pnpm vitest --run still reports the existing 4 RLS failures in src/rls/index.test.ts; the new SQL macros test file passes in the full run

Notes

This is a non-overlapping coverage slice for #71, separate from the Stripe, WebSocket, Clerk, and CDC plugin test PRs I submitted earlier.