Return Cow instead of String from chunkid

[Shatur]

Pull Request

Summary

Avoid allocations if possible in chunkid.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing
  functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test improvements
• Build system/dependency changes

Related Issues

Closes #47.

Fixes #(issue number)

Testing

cargo test passes.

Tested On

• Linux
• macOS
• Windows

Quality Checklist

• Code follows project style guidelines
• Self-review of code completed
• Tests pass locally
• Documentation updated (if applicable)

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By submitting this PR, I confirm that:

• I have read and agree to the Contributing Guidelines
• I am willing to address feedback and make necessary changes