fix: discrepancies on file source detection

[Sec-ant]

Summary

Fix discrepancies on file source detection. Allow module syntax in .cts files.

Fixes #2114.

Test Plan

Added a test case to show that the following statement can be used in a .cts file:

export default { cjs: true };

[netlify]

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Lighthouse	1 paths audited Performance: 100 (🟢 up 4 from production) Accessibility: 97 (no change from production) Best Practices: 100 (no change from production) SEO: 93 (no change from production) PWA: - View the detailed breakdown and full score reports

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[codspeed-hq]

CodSpeed Performance Report

Merging #2116 will not alter performance

_{Comparing Sec-ant:fix/file-source-detection (921858f) with main (984626d)}

Summary

✅ 93 untouched benchmarks

[togami2864]

Thank you!