[Ghraven]

Summary

• read and write generated test-case JSON files with explicit UTF-8 encoding
• read dynamic pytest test-case JSON fixtures with the same encoding

Before / after

Before, the CLI test-case generator and load_test_cases() relied on the platform default text encoding for JSON fixture files.
After, both paths use UTF-8 explicitly, making generated fixtures portable across non-UTF-8 locales.

Verification

• python -m py_compile burr/cli/__main__.py burr/testing/__init__.py
• git diff --check

[andreahlert]

LGTM following #790

[github-actions]

This PR has had no activity for 96 days.
Closing to keep the PR list manageable.

Feel free to reopen when you are ready to continue.
If the branch has conflicts, a fresh PR against main might be easier.