Describe the issue:
When making a submission using the CLICS 2023-06 API (eg. pc2submit Python command line utility), source files should be sent as a single ZIP file encoded as BASE64. The current implementation does not create a ZIP file, rather, it encodes each file as a separate BASE64 string and passes them as CLICSFileReferenceObjects.

In addition, the pc2submit Python utility should be fixed to put the source files for the submission in a single ZIP file, BASE64 encode that zip file, and pass that along to theserer

To Reproduce:
Try to make a submission using a CLICS compliant command line submit utility that packages the source file(s) up as a single ZIP encoded as BASE64.

Expected behavior:
Submissions made to the CLICS submissions endpoint should accept a BASE64 encoded ZIP file containing the source code for the submission.

Actual behavior:
Submissions made to the CLICS submissions endpoint will fail if the submission is a BASE64 encoded ZIP file containing the source code for the submission.

Environment:
All.

Log Info:

Screenshots:
Additional context:
This issue was pointed out indirectly by he DOMjudge folks. They attempted to make a submission using the pc2submit utility we modified to be CLICS 2023-06 compliant to the DOMjudge system. It failed because the CLICS specification unclearly indicates that the array of FILE included in the submission should be a single BASE64 encoded ZIP file. The ZIP file contains the source code for the submission.