fix: install turbo as optional dependency

[Manussakis]

Description of the Change

Closes #617

How to test the Change

Run npm install from machines with different architectures and platforms:

• Darwin x64
• Darwin arm64
• Linux x64
• Linux arm64
• Windows x64
• Windows arm64

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests pass.

[changeset-bot]

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Latest commit: 613566b

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[github-actions]

📦 Next.js Bundle Analysis for @10up/headless_framework

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