Replace Qt RegEx with Python RegEx

[vkbo]

Summary:

This PR replaces QRegularExpression from Qt with Python's standard library regex module.

There are two reasons for doing this:

• The standard library one is a little bit faster, mostly because there is no need to convert strings when calling it like is needed for the Qt one (I suspect that's the reason anyway).
• The PyQt6 interface th QRegularExpression is broken, at least for Qt 6.4.2. The returned matches are sometimes garbled. Presumably due to UTF-16 to UTF-8 conversion, but I'm not sure. Switching to the Python implementation avoids this problem in the future when we switch to Qt6.

Related Issue(s):

Reviewer's Checklist:

• The header of all files contain a reference to the repository license
• The overall test coverage is increased or remains the same as before
• All tests are passing
• All flake8 checks are passing and the style guide is followed
• Documentation (as docstrings) is complete and understandable
• Only files that have been actively changed are committed