Config revision

[forman]

• Introduced type aliases ConfigLike and ConfigObjectLike.
• Renamed multiple components for improved clarity and consistency:
  • Renamed Config into ConfigObject
  • Renamed ConfigList.configs into config_objects
  • Renamed ConfigList into Config
  • Renamed ConfigList.compute_config() into compute_config_object()
  • Renamed Result.config into config_object
  • Renamed XRLint.load_config_list() into init_config()
  • Renamed XRLint.verify_datasets() into verify_files()
• Added class method from_config() to ConfigList.
• Removed function xrlint.config.merge_configs as it was no longer used.

Checklist (strike out non-applicable):

• Changes documented in CHANGES.md
• Related issue exists and is referred to in the PR description and CHANGES.md
• Added docstrings and API docs for any new/modified user-facing classes and functions
• Changes/features documented in docs/*
• Unit-tests adapted/added for changes/features
• Test coverage remains or increases (target 100%)