Meta-issue - Feature: scoring probabilistic and point forecasts together / composing scores

[nikosbosse]

We would like to be able to score probabilistic forecasts along with point forecasts. Then, all metrics should be composed to a final data.table.

This could involve a workflow like this one:

scores_probabilistic <- example_continuous |>
  score()

scores_point <- example_continuous |>
  as_point(statistic = "median") |>
  score()

scores <- c(scores_probabilistic, scores_point)

• Create function as_point() that converts sample- or quantile-based forecasts into point forecasts #432
• Discussion: composing score data.frames #434