feat(esm): Test esm template dirs in packages/create-cedar-app

[Tobbe]

Introduce the same kind of tests we already have for the standard template files also for the new esm template files

4/n in a long line of ESM prep PRs that started with #349

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[greptile-apps]

Greptile Summary

This PR adds snapshot tests for two new ESM (ECMAScript Modules) template directories in the create-cedar-app package. The changes introduce test coverage for esm-ts and esm-js templates, which are modernized versions of the existing TypeScript and JavaScript templates.

The key additions include:

• New path constants for the ESM template directories (ESM_TS_TEMPLATE_DIR and ESM_JS_TEMPLATE_DIR)
• Snapshot tests that capture the expected file structure for both ESM templates
• Documentation of the migration from Jest to Vitest in these templates, evidenced by the replacement of jest.config.js files with vitest.config.ts/js files and the addition of vitest.setup.ts/js files

These tests follow the established pattern used for existing template tests, using inline snapshots to detect unintentional changes to the template structure. This ensures that when users run create-cedar-app with ESM templates, the scaffolding process maintains consistency and doesn't break due to structural changes. The ESM templates represent a modernization effort, embracing native ES modules and Vitest for testing, which aligns with current JavaScript ecosystem trends.

Confidence score: 4/5

• This PR is safe to merge with minimal risk as it only adds test coverage without modifying template functionality
• Score reflects straightforward test additions following established patterns, with clear benefits for template integrity
• Pay close attention to the snapshot content to ensure it accurately reflects the intended ESM template structure

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