BOT: Fix #975: Add print.scores() S3 method with metrics and vignette link

[nikosbosse]

Summary

• Adds a print.scores() S3 method that displays the names of scoring metrics used and a link to the scoring rules vignette before printing the underlying data.table
• Follows the existing print.forecast() pattern: uses cli_text() for formatted output, calls NextMethod() for data.table printing, returns x invisibly
• Handles edge cases gracefully: missing metrics attribute (skips metrics display), renamed columns (warning via get_metrics.scores())

Closes #975
Related to #667

Root cause

Scores objects had no custom print method — they fell through to print.data.table(), providing no context about which scoring rules were used or where to find their definitions.

What changed

• R/class-scores.R: New print.scores() S3 method that displays "Metrics: ..." and "Score definitions: " before delegating to data.table print
• tests/testthat/test-class-scores.R: 6 new tests covering metrics display, vignette link, all forecast types, invisible return, data.table delegation, missing attributes, and renamed columns
• tests/testthat/_snaps/class-forecast-multivariate-sample.md: Updated snapshot to include new print output
• NAMESPACE / man/print.scores.Rd: Auto-generated exports and documentation

Test plan

• 6 new tests for print.scores() covering core functionality and edge cases
• Full test suite passes (725 tests, 0 failures)
• R CMD check: 0 errors, 0 warnings, 2 notes (pre-existing)
• Snapshot test updated for multivariate sample scores

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.84%. Comparing base (ac0c01a) to head (8ace320).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1078      +/-   ##
==========================================
+ Coverage   97.83%   97.84%   +0.01%     
==========================================
  Files          35       35              
  Lines        1845     1856      +11     
==========================================
+ Hits         1805     1816      +11     
  Misses         40       40              

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[nikosbosse]

CLAUDE: Clean, well-scoped implementation that follows the existing print.forecast() pattern exactly. The method correctly displays metric names and a vignette link before delegating to data.table printing, with proper edge case handling (missing metrics attribute, renamed columns). All 6 tests match the specifications and cover core functionality plus edge cases. Two minor cosmetic nits (unnecessary #nolint annotation on URL cli_text block, \dontrun example could be runnable) — neither blocking. Verdict: approve.