Add support for python 3.13

[almet]

Python 3.13 is available since Oct. 7, 2024. The reason we don't support it is because PySide6 didn't support it yet. They announced support for Python 3.13 will be added in Pyside6 6.8. .

But... I've been able to run it locally with the latest pyside6==6.8.0.1 release, so I wonder if we could get away with it:

> uv venv .venv -p python3.13
> uv pip install pyside6
Resolved 4 packages in 892ms
Prepared 4 packages in 38.00s
Installed 4 packages in 35ms
 + pyside6==6.8.0.2
 + pyside6-addons==6.8.0.2
 + pyside6-essentials==6.8.0.2
 + shiboken6==6.8.0.2

And then running a small UI from their doc, here if you want:

import sys
import random
from PySide6 import QtCore, QtWidgets, QtGui


class MyWidget(QtWidgets.QWidget):
    def __init__(self):
        super().__init__()

        self.hello = ["Hallo Welt", "Hei maailma", "Hola Mundo", "Привет мир"]

        self.button = QtWidgets.QPushButton("Click me!")
        self.text = QtWidgets.QLabel("Hello World", alignment=QtCore.Qt.AlignCenter)

        self.layout = QtWidgets.QVBoxLayout(self)
        self.layout.addWidget(self.text)
        self.layout.addWidget(self.button)

        self.button.clicked.connect(self.magic)

    @QtCore.Slot()
    def magic(self):
        self.text.setText(random.choice(self.hello))


if __name__ == "__main__":
    app = QtWidgets.QApplication([])

    widget = MyWidget()
    widget.resize(800, 600)
    widget.show()

    sys.exit(app.exec())

We currently fallback on Pyside2 in our code, when PySide6 isn't installed, which should be the case on systems where Python is older than Python3.11. We would probably need to trick the debian and fedora package building scripts to replace the python 3.13 dep with something older.