fix: handle multipart uploads with >1000 parts for AWS/RadosGW

[mesemus]

Description

This PR fixes failing multipart upload for very large files to AWS or RadosGW.

• For very large files (hundreds of GB), multipart uploads in the current UI uploader can exceed
  1000 parts
• Unlike MinIO, AWS and RadosGW part listings return at most 1000 parts per response. Code
  now handles pagination to retrieve all parts
• Added manual test to verify the fix (disabled by default). MinIO's implementation differs by
  returning full listings unconditionally and cannot be used to test the fix.

→ See test_multipart.py for manual test execution details

Checklist

Ticks in all boxes and 🟢 on all GitHub actions status checks are required to merge:

• I'm aware of the code of conduct.
• I've created logical separate commits and followed the commit message format.
• I've added relevant test cases.
• I've added relevant documentation.
• I've marked translation strings.
• I've identified the copyright holder(s) and updated copyright headers for touched files (>15 lines contributions).
• I've NOT included third-party code (copy/pasted source code or new dependencies).
  • If you have added third-party code (copy/pasted or new dependencies), please reach out to an architect on Discord.

Frontend

• I've followed the CSS/JS and React guidelines.
• I've followed the web accessibility guidelines.
• I've followed the user interface guidelines.

Reminder

By using GitHub, you have already agreed to the GitHub’s Terms of Service including that:

1. You license your contribution under the same terms as the current repository’s license.
2. You agree that you have the right to license your contribution under the current repository’s license.

[wgresshoff]

This looks very good to me, great you added a test for >parts as well!