feat: improve checkstyle report, added metrics entries

[dkrutskikh]

What is the purpose of this pull request? (put an "X" next to an item)

[ ] Documentation update
[ ] Bug fix
[ ] New rule
[ ] Changes an existing rule
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

Potentially close #842

What changes did you make? (Give an overview)

Is there anything you'd like reviewers to focus on?

[github-actions]

Dart Code Metrics unused files report of dart_code_metrics. ✅

Summary

• Scanned package folders: bin, example, lib
• No unused files found! ✅

[github-actions]

Dart Code Metrics analyze report of dart_code_metrics. ✅

Summary

• Scanned folders: bin, example, lib, test

• Total scanned files: 430

• Total lines of source code: 7557

• Total classes: 296

• Average Cyclomatic Number per line of code: 0.35

• Average Source Lines of Code per method: 6

• Total tech debt: 1326.0 hours

• Found issues: 6 ⚠

[codecov]

Codecov Report

Merging #896 (1dbbf43) into master (75e0fb7) will increase coverage by 0.05%.
The diff coverage is 97.43%.

@@            Coverage Diff             @@
##           master     #896      +/-   ##
==========================================
+ Coverage   87.37%   87.43%   +0.05%     
==========================================
  Files         283      283              
  Lines        5997     6024      +27     
==========================================
+ Hits         5240     5267      +27     
  Misses        757      757              

Impacted Files	Coverage Δ
...ters_list/checkstyle/lint_checkstyle_reporter.dart	98.07% <97.43%> (+2.07%)	⬆️

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