Issue 272: Add an across argument to summarise_scores()

[seabbs]

This PR closes #272 by implementing an across argument to summarise_scores().

It also:

• Updates the release version by one minor release (in line with other recent PRs)
• Adds a news item for this change
• Adds an example to the summarise_scores() documentation for this new argument.
• Adds tests that check the equivalence of this approach as well as checking it errors when expected.

Note that because of the multiple duplicate variables in the example data across isn't actually as useful as you might imagine (i.e. because target_end_date and horizon define the same thing).

[codecov]

Codecov Report

Merging #302 (41602c6) into main (3bf41d8) will increase coverage by 0.07%.
The diff coverage is 100.00%.

❗ Current head 41602c6 differs from pull request most recent head 0f9150b. Consider uploading reports for the commit 0f9150b to get more accurate results

@@            Coverage Diff             @@
##             main     #302      +/-   ##
==========================================
+ Coverage   89.61%   89.68%   +0.07%     
==========================================
  Files          22       22              
  Lines        1367     1377      +10     
==========================================
+ Hits         1225     1235      +10     
  Misses        142      142              

Impacted Files	Coverage Δ
R/summarise_scores.R	83.33% <100.00%> (+1.93%)	⬆️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[nikosbosse]

Thanks! Looks good to me. Only minor point is that we might want to add a warning if there are column names in across that aren't in the data.

[seabbs]

I extended the do any of the across variables check to cover are any not in the forecast unit. I also added some verbosity to the documentation.

[nikosbosse]

Nice, looks good! There is just one word or something in the documentation missing, otherwise happy to merge

[seabbs]

Reworded. Give it a review and will merge when okay'd

[nikosbosse]

Not sure how strongly you feel about linter complaints :D
Happy to merge from my side :)