Write metric_ids and metric_values as lists

[rcannood]

Describe your changes

file_score.yaml declares both metric_ids and metric_values as multiple: true, and common/schemas/results_v4/results.json types the corresponding metric_names/metric_values as arrays. Two metrics write them as scalars instead:

• metrics/average_batch_r2 -- "metric_ids": "average_batch_r2_ct", "metric_values": average_batch_r2_ct
• metrics/flowsom_mapping_similarity -- metric_ids = "flowsom_mean_mapping_similarity", metric_values = fs_mapping_similarity_avg (a length-1 R vector, which reticulate hands to anndata as a plain Python string/float)

The other four metric components already write lists. This PR makes these two do the same, so the score files are consistent and the results schema holds for every component.

Found while reviewing the task ahead of the next full benchmark run -- see also the sibling PRs.

Checklist before requesting a review

• I have performed a self-review of my code

• Check the correct box. Does this PR contain:

  • Breaking changes
  • New functionality
  • Major changes
  • Minor changes
  • Bug fixes

• Proposed changes are described in the CHANGELOG.md

• CI Tests succeed and look good!

[rcannood]

The previous notation was ok, but let's go for it anyways