removed deprecated xpress methods

[RobbieKiwi]

Closes #533

Changes proposed in this Pull Request

Removed old xpress methods and replaced them with the new ones

Checklist

• A note for the release notes doc/release_notes.rst of the upcoming release is included.
• I consent to the release of this PR's code under the MIT license.

[RobbieKiwi]

It works on my computer, I don't know how to set up testing with these licensed solvers

[RobbieKiwi]

I noticed another issue
Xpress 9.5 does not work since the latest release of linopy (0.5.8), I have a look into this as well

File "d:\RMU\PythonProjects\SmaOpt\.venv\Lib\site-packages\linopy\solvers.py", line 1608, in get_solver_solution var = m.getnamelist(xpress.Namespaces.COLUMN, 0, m.attributes.cols - 1) ^^^^^^^^^^^^^^^^^ File "d:\RMU\PythonProjects\SmaOpt\.venv\Lib\site-packages\xpress\__init__.py", line 157, in __getattr__ raise AttributeError("module '%s' has no attribute '%s'" % (__name__, name)) AttributeError: module 'xpress' has no attribute 'Namespaces'