feat(skore): limit a project to a single `ML task`

[thomass-dev]

Closes https://github.com/probabl-ai/skore-hub/issues/852.

As a user:

• in an empty project, i can add a report with any ML task (report.ml_task)
• in a non-empty project, i can only add a report with the same ML task as the previously added report
  • an exception is raised when this condition is not met

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In technical terms, in the skore.Project class:

• during the project initialization, request the project summary to retrieve the list of ML task
  • raise an exception if the list is not uniform
• every time i put a report, i compare its ML task to the one retrieved previously
  • raise an exception if different

[auguste-probabl]

Maybe Project could have a ml_task attribute then?

[thomass-dev]

Yes, it was somewhat implied in

during the project initialization, request the project summary to retrieve the list of ML task

You can create an attribute with the result of the summary inspection.