create parent directory before writing digest files

[vivek-26]

Fixes #813

Description
Create parent directory before writing digest files.

Submitter Checklist

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• Includes unit tests
• Adds integration tests if needed.

Reviewer Notes

• The code flow looks good.
• Unit tests and or integration tests added.

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[vivek-26]

@googlebot I signed it!

[vivek-26]

@priyawadhwa PTAL