Improve docstring/signature of objects to help users

[GaelVaroquaux]

Is your feature request related to a problem? Please describe.

As I work using skore on vscode, this is what I see when trying to use the CrossValidationReporter:

The problem with this display is that it does not tell me what are the arguments to CrossValidationReporter, which is the most important information that I need as a user

Same problem with skore.Project: I just cannot easily figure out what I need to specify as a list of arguments

Describe the solution you'd like

I want to guess what to type looking at what vscode shows me :)

Describe alternatives you've considered, if relevant

No response

Additional context

No response

[MarieS-WiMLDS]

About CrossValidationReporter, we have an issue for this: #953.

It seems that you want to create a project by doing skore.Project, which is actually very legit. We have a create function for that, but now I wonder why. It's documented in this (long) issue #917.