feat: include issue/PR numbers under contribution types

[JoshuaKGoldberg]

PR Checklist

• Addresses an existing open issue: fixes feat: include issue/PR numbers under contribution types #13
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

Changes the output format as suggested in #13:

{
-  joshuakgoldberg: [ 'maintenance', 'tool' ],
+  joshuakgoldberg: { maintenance: [123], tool: [456, 789] }
}

[codecov]

Codecov Report

Merging #13 (d30cdd9) into main (56ad0c1) will increase coverage by 3.67%.
The diff coverage is 47.05%.

@@            Coverage Diff             @@
##             main      #13      +/-   ##
==========================================
+ Coverage   32.46%   36.14%   +3.67%     
==========================================
  Files          11       13       +2     
  Lines          77       83       +6     
  Branches       13       14       +1     
==========================================
+ Hits           25       30       +5     
- Misses         52       53       +1     

Impacted Files	Coverage Δ
src/collect/collectEvents.ts	0.00% <ø> (ø)
src/collect/index.ts	0.00% <0.00%> (ø)
src/createAllContributorsForRepository.ts	0.00% <0.00%> (ø)
src/ContributorsCollection.ts	88.88% <80.00%> (-11.12%)	⬇️
src/Contributor.ts	100.00% <100.00%> (ø)
src/collect/eventIsPullRequestReviewEvent.ts	100.00% <100.00%> (ø)

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