Proposed changes

This PR addresses an inconsistency in the "Pure Functions" subsection of the mlx.compile documentation.

The guide currently mentions two methods for capturing mutable external state, but only provides a code example for the second method.

Problem: The text states, "The first option is to simply pass state as input to the function," but this method was not demonstrated with code.

Solution: This change inserts the missing code block, which explicitly shows the technique of passing state as an argument. This provides a clear contrast between the two options and improves the overall clarity and completeness of the documentation section.

Checklist

Put an x in the boxes that apply.

• I have read the CONTRIBUTING document
• I have run pre-commit run --all-files to format my code / installed pre-commit prior to committing changes
• I have added tests that prove my fix is effective or that my feature works
• I have updated the necessary documentation (if needed)