Meta-issue: Code refactoring

[nikosbosse]

This meta issue tracks ideas to refactor the code to make it more efficient / cleaner.

Outstanding issues:

• Code refactoring: Deduplicate code in get_coverage() and interval_coverage_deviation_quantile() #454
• Rework interval_coverage_sample() #411
• Cleanup: delete calls that use :: or ::: and add to imports instead #445
• Replace delete_columns()? #446
• Refactor: simplify data validation in score() #469

Potential changes to be discussed that don't have an issue yet:

• Could create a helper function that checks whether dimensions match in sample-based and quantile-based forecasts, analogously to what was done in Update input formats for binary and point forecasts #460 for point and binary forecasts