Bug Report Checklist

• I have tried restarting my IDE and the issue persists.
• I have pulled the latest main branch of the repository.
• I have searched for related issues and found none that matched my issue.

Overview

tsup isn't maintained anymore. It's got bugs. tsdown is the roughly community-anointed successor.

Additional Info

Corresponding CTA issue: JoshuaKGoldberg/create-typescript-app#2223

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