fix(next-transpile-modules): use pnpm for pretest setup

[riceharvest]

Summary

• Switches next-transpile-modules pretest setup from npm to pnpm so pnpm workspace config is not passed through npm.
• Adds a regression test for the package-local pretest script.

Tests

• corepack pnpm@9.6.0 --filter @opensourceframework/next-transpile-modules test
• corepack pnpm@9.6.0 --filter @opensourceframework/next-transpile-modules run typings
• corepack pnpm@9.6.0 exec eslint packages/next-transpile-modules/test/package-scripts.test.ts
• corepack pnpm@9.6.0 exec prettier --check packages/next-transpile-modules/test/package-scripts.test.ts
• git diff --check

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