Issue #383 - Remove available_metrics()

[nikosbosse]

Description

This PR closes #383

available_metrics() is a remnant of the sunnier days when scoringutils had a restricted list of known metrics. Now that users can specify their own metrics, the function is not needed anymore and should be removed.

This PR

• removes available_metrics()
• to do this plot_correlations() needed to be updated which relied on it. avaiable_metrics() is now changed to get_score_names()
• for that to work, the input to plot_correlations() has to have a score_names attribute. The PR therefore updates correlation() to output a scores object with the necessary score_names attribute
• since the original correlation() outputs a data.table with rownames, new_scores() was updated to now have a ... argument which is used within correlation to specify keep.rownames = TRUE. Within correlation there is now an explicit copy statement, because without that we're getting an internal self reference error (data.table isn't happy about the rownames...). I feel like this is sufficient to address the issue here and always making a copy at the end of new_scores() might be an overkill
• updates a few tests
• removes available_metrics() from get_protected_columns()

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The data.table copy issue should maybe be an issue for data.table...
Reprex:

x <- data.frame(x = 1:10, row.names = paste0("test_", 1:10))
x <- as.data.table(x, keep.rownames = TRUE)
class(x) <- c("test", class(x))
x[, testtest := 1]

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Checklist

• My PR is based on a package issue and I have explicitly linked it.
• I have included the target issue or issues in the PR title as follows: issue-number: PR title
• I have tested my changes locally.
• I have added or updated unit tests where necessary.
• I have updated the documentation if required.
• I have built the package locally and run rebuilt docs using roxygen2.
• My code follows the established coding standards and I have run lintr::lint_package() to check for style issues introduced by my changes.
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• I have reviewed CI checks for this PR and addressed them as far as I am able.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.28%. Comparing base (a45f4f5) to head (8a18e16).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #706      +/-   ##
==========================================
- Coverage   95.28%   95.28%   -0.01%     
==========================================
  Files          21       21              
  Lines        1634     1632       -2     
==========================================
- Hits         1557     1555       -2     
  Misses         77       77              

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[seabbs]

All seems sensible to me. Agree on copy.