Fix shear transformation for multiple axes (#8450)

[EloiNavet]

Fixes #8450 by proper shear composition.

Description

A few sentences describing the changes proposed in this pull request.

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• Integration tests passed locally by running ./runtests.sh -f -u --net --coverage.
• Quick tests passed locally by running ./runtests.sh --quick --unittests --disttests.
• In-line docstrings updated.
• Documentation updated, tested make html command in the docs/ folder.

[Copilot]

Pull Request Overview

This pull request addresses the incorrect shear transformation calculation in 2D by updating the matrix composition.

• Updated the shear composition for 2D transformations by modifying the identity matrix accordingly.
• Fixed the shear coefficient application by adjusting the second diagonal element.

[ericspod]

Hi @EloiNavet thanks for the submission but this does change behaviour significantly as you see in the tests. I realise the shearing behaviour isn't correct but it would change results for a number of tests as well as those we'd see in tutorials. We may need some way of preserving the old behaviour while offering the new fixed behaviour as well.