Fix Cybersixgill mentions API call

[aloftus23]

fixes #361
During the latest report run, we noticed random error responses from the intel_items API endpoint.

🗣 Description

Current process: We first get the total number of mentions, then pull down each specific mention in segments of 100. Most of the time, a segment of 100 successfully responds. On failure, the segment is skipped.

Therefore, we redesigned the code to pull down the mentions in segments of 100, then try 10, then try 1. Calling the API in segments of 1 is yet to fail. After 10 iterations of a smaller segments, the rest will try 100 again to speed up the process.

🧪 Testing

All pytests and pre-commits pass. Confirmed no errors in a full report run.

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All future TODOs are captured in issues, which are referenced
  in code comments.
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• These code changes follow cisagov code standards.
• All relevant repo and/or project documentation has been updated
  to reflect the changes in this PR.
• Tests have been added and/or modified to cover the changes in this PR.
• All new and existing tests pass.