fix: Add missing numpy dependency

[grossjct]

Fixes #452

Changes proposed in this pull request:

• add missing numpy dependency

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[Copilot]

Pull request overview

Adds the missing numpy dependency to the bench optional dependency group so olmocr.bench can be run without a ModuleNotFoundError (Fixes #452).

Changes:

• Add numpy to [project.optional-dependencies].bench in pyproject.toml.

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

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