fix(highlight): improve table checking

[fannheyward]

Related #5416

[Copilot]

Pull Request Overview

This PR improves the table checking logic in the highlight_ranges function by adding a type check to ensure the opts parameter is a table before proceeding with its usage.

• Replaces simple null check with combined null and type validation for the opts parameter
• Ensures opts is always a valid table before accessing its properties

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.99%. Comparing base (1807db6) to head (efb1e6b).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5417   +/-   ##
=======================================
  Coverage   97.99%   97.99%           
=======================================
  Files         280      280           
  Lines       27862    27862           
  Branches     5768     5768           
=======================================
  Hits        27302    27302           
  Misses        102      102           
  Partials      458      458           

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