Remove un-needed Arc around IndexPart in initialization

[jcsp]

Problem

Summary of changes

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

1624 tests run: 1550 passed, 0 failed, 74 skipped (full report)

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_{The comment gets automatically updated with the latest test results
37cf478 at 2023-08-23T15:58:52.030Z :recycle:}