Fix release declaration build with TypeScript 6

[kentcdodds]

Summary

• remove the deprecated --downlevelIteration flag from the release declaration build command
• add inline JSDoc typing for the shared globalThis.__remember_epic_web map so TypeScript 6 can emit declarations
• keep the generated public declaration surface limited to the existing remember / forget exports

Testing

• npx -p typescript tsc --declaration --emitDeclarationOnly --allowJs --checkJs --module nodenext --moduleResolution nodenext --target es2022 --outDir . index.js
• npx bun test
• GitHub Actions 📦 Build release artifact passed on branch push
• GitHub Actions 🧪 Test passed on both branch push and PR runs