Test refactor changes builder

[dariomesic]

Purpose

This PR resolves the TODO in test_build_changes.py which suggested using better HTML content checking.

The previous test implementation used simple string in htmltext assertions. This method is brittle and can easily fail if HTML tags, CSS classes, or attributes are changed in the future.

This commit refactors the test_build function to:

1. Parse the generated HTML using BeautifulSoup.
2. Validate the document structure, not just the raw text.
3. Introduce a find_change_item helper function to make the test cleaner, more robust, and easier to maintain.

This makes the test more resilient to future template changes.