BOT: Fix #363: Add metric adapter functions for external scoring metrics

[nikosbosse]

Summary

• Adds metric_adapt_binary_numeric() — wraps external metrics that expect numeric 0/1 observed values, converting the factor input that scoringutils uses for binary forecasts
• Adds metric_adapt_swap_args() — wraps external metrics with function(predicted, observed) signature to match scoringutils' function(observed, predicted) convention
• Both adapters return functions with (observed, predicted, ...) formals, compatible with score(), run_safely(), and purrr::partial()

Fixes #363

Root cause

Users cannot directly use external scoring functions in score() when those functions expect a different argument order or numeric (not factor) binary observed values. purrr::partial() can fix extra parameters but cannot reorder positional arguments or perform type conversion.

What this does

Creates two small adapter/wrapper factory functions that return closures with the correct signature. The adapters:

• Convert factor observed to 0/1 numeric (metric_adapt_binary_numeric)
• Swap the first two positional arguments (metric_adapt_swap_args)
• Pass through ... for additional parameters
• Are composable with purrr::partial() for further customization

Test coverage

10 test cases covering:

• Basic factor-to-numeric conversion
• End-to-end integration with score() for binary, point, and sample forecasts
• Argument order reversal verification
• Function object properties (formals, ... pass-through)
• Composability with purrr::partial()
• Input validation (non-function inputs error)
• Extra argument pass-through

Test plan

• New adapter tests pass (26 expectations)
• Full test suite passes (704 tests, 0 failures)
• R CMD check: 0 errors, 0 warnings, 2 pre-existing notes

🤖 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 (889e308).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1101      +/-   ##
==========================================
+ Coverage   97.83%   97.84%   +0.01%     
==========================================
  Files          35       36       +1     
  Lines        1845     1854       +9     
==========================================
+ Hits         1805     1814       +9     
  Misses         40       40              

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[nikosbosse]

CLAUDE: Approve — Clean, minimal implementation of two adapter factory functions (metric_adapt_binary_numeric and metric_adapt_swap_args) that solve a real usability gap for external metric integration. Code follows existing package patterns (identical factor conversion to brier_score), closures have correct formals for run_safely() compatibility, and the 10-test suite covers unit, integration, composability, validation, and pass-through scenarios. No issues found.