PR summary

A mini simplification in ContourSet.draw: now that Collection.set_paths exists (#26342), we can push the path setting into the _cm_set context manager with everything else.

PR checklist

• "closes #0000" is in the body of the PR description to link the related issue
• new and changed code is tested
• Plotting related features are demonstrated in an example
• New Features and API Changes are noted with a directive and release note
• Documentation complies with general and docstring guidelines