[typescript-migration] some tests and configs

[yuki0410-dev]

Description

Linked issue: #4700

Changes

• migrate src/test/datepicker_test.test.tsx
• migrate src/test/helper_components/custom_input.tsx
• migrate rollup.config.mjs

Contribution checklist

• [x] I have followed the contributing guidelines.
• [x] I have added sufficient test coverage for my changes.
• [x] I have formatted my code with Prettier and checked for linting issues with ESLint for code readability.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.65%. Comparing base (0728d1f) to head (0263278).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #4891 +/- ## ======================================= Coverage 96.64% 96.65% ======================================= Files 28 28 Lines 3251 3254 +3 Branches 1354 1342 -12 ======================================= + Hits 3142 3145 +3 - Misses 105 109 +4 + Partials 4 0 -4 ```

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