feat: Migrate from `base64-js`

[d-goog]

It's unmaintained with no releases for 5+ years:

• https://www.npmjs.com/package/base64-js?activeTab=versions

Implementation Notes:

• This functionality from used from the library may exist in JS itself now. Perhaps here's a good starting point for research:
  • https://developer.mozilla.org/en-US/docs/Glossary/Base64
  • https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array
    • polyfill implementation:
      • https://github.com/zloirock/core-js/blob/2712a2b845ed8a1bc3936e3ff2b2817cd7ebb7dc/packages/core-js/modules/esnext.uint8-array.to-base64.js#L19
      • https://github.com/zloirock/core-js/blob/2712a2b845ed8a1bc3936e3ff2b2817cd7ebb7dc/packages/core-js/modules/esnext.uint8-array.from-base64.js