Fix FutureWarning in infer_categorical_columns by converting list to numpy array

[pragati-0208]

Summary

This PR fixes a FutureWarning from pandas that occurs when pd.unique() is called on a list input in the infer_categorical_columns function. The warning indicates that list inputs will be rejected in future pandas versions.

Changes Made

• Modified nwbwidgets/utils/dynamictable.py
• Convert list to numpy array before calling pd.unique()
• Maintains all existing functionality while eliminating the warning

Motivation

• Eliminates distracting warnings during test execution
• Ensures compatibility with future pandas versions
• Follows pandas best practices for array handling

Testing

• All existing tests pass (114 passed, 1 skipped)
• No changes to function behavior
• Warning no longer appears in test output

Related Issues

This addresses warnings seen in the test suite output.

Checklist

• Code follows project style guidelines
• Tests pass locally
• No breaking changes to existing functionality