Submission problem score - Serializer

[alans-42]

Proposed changes

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This pull request adds the serializer and test for the submission problem score. Closes #12

Types of changes

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What types of changes does your code introduce?
Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist

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Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. This is simply a reminder of what we are going to look for before merging your code.

• My changeset covers only what is described above (no extraneous changes)
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works (Refer to further comments)
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged downstream

Further comments

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[alans-42]

Made this a draft because I still need to test my tests when SubmissionProblemScore is fully implemented