Adapt package to reorganized backend #2

Description

This issue addresses the recent breaking changes in the structure of the backend. This included renaming concepts, changing endpoints, and enhancing authentication. Without addressing these changes in this package, the client will not be able to connect to the cloud engine anymore and will drift from the general concepts of the overall system.

Tasks

• Rename modules: activities.py → predictions.py and tasks.py → targets.py, with the matching test files and scripts
• Rename concepts: every Activity*/Task* name became Prediction*/Target*
• Adjust paths: the endpoints are /api/v1/predictions, /api/v1/predictions/shares and /api/v1/targets, without trailing slashes
• Implement lab predictions: Prediction.space_id is now optional and the models carry lab_id and lab_name. Before, a single lab prediction in a page made predictions.list() fail.
• Implement media dimensions: predictions.create() takes width, height and duration_seconds. analyze() reads them from the file header, so the API reserves the real token cost