Replaced VSCode with Positron (and conda with pixi)

[pdallago97]

I have replaced the VSCode parts with Positron. The conda installations have been replaced with the pixi intsallations.

I think only two screenshots actually need replacement, the rest (all the Git part) is really the same as the previous one (even if in VSCode).

I also felt like reordering bits of code/text, as it was clearer to me.

I have added minor things such as the command ls -a in 'using pixi' to see all files (as ls only does not show all the hidden files).

Things to note:
the cow.py example gives a warning (only the first time you run it).
Disable GitHub Copilot: disabling the settings for GitHub Copilot: Enable should be enough? When looking for GitHub Copilot Chat a loooot of settings are found.
The Extensions are already installed in the VM. I changed the text to make the students note that these are installed, but no installments are done.
Positron raises an error when calling a package MyPackage, it suggests calling it my_package and solves the problem.
I removed the extensions.png image as it was the same as main.py ? no need to repeat twice?