feature/create pr 2

[MStupar-nc]

Add "list unread" command to book app

This PR adds a new feature to the sample book app:

• BookCollection.get_unread_books(): returns unread books (read == False).
• CLI: adds "unread" and "list-unread" commands handled by handle_unread(), reusing existing show_books() output.
• Tests: comprehensive pytest tests for get_unread_books covering ordering, empty states, and mixed read/unread behavior.
• Added samples/book-app-project/plan.md describing the planned work.

Files changed:

• samples/book-app-project/books.py (+get_unread_books)
• samples/book-app-project/book_app.py (+handle_unread, help text, command registration)
• samples/book-app-project/tests/test_books.py (+tests for unread filtering)
• samples/book-app-project/plan.md (new)

Notes:

• Method named get_unread_books to keep implementation explicit and testable. Consider renaming to list_unread() for API symmetry.

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com