test(upload-client): allow large byte uploads

[StefanoDeVuono]

There was an issue with large byte uploads in tests highlighted in issue 1518

This commit fixes the issue by first converting bytes to UnixFS stream before making CAR object in packages/upload-client/test/helpers/car.js.

Included is a video of the tests passing with both the current byte size (128) and the previously failing byte size (2_000_0000):

https://github.com/user-attachments/assets/b24e41b5-d8c7-4252-a7c8-2a49ae6f6037