feat: add static code diagnostic avoid-redundant-async

[incendial]

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:

#113

[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: 503

• Total lines of source code: 8639

• Total classes: 374

• Average Cyclomatic Number per line of code: 0.36 / 1

• Average Source Lines of Code per method: 6

• Total tech debt: 2130.0 hours

• Found issues: 6 ⚠

[codecov]

Codecov Report

Merging #1002 (305a3c1) into master (a254d6e) will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1002      +/-   ##
==========================================
+ Coverage   87.41%   87.48%   +0.06%     
==========================================
  Files         313      315       +2     
  Lines        6620     6657      +37     
==========================================
+ Hits         5787     5824      +37     
  Misses        833      833              

Impacted Files	Coverage Δ
...c/analyzers/lint_analyzer/rules/rules_factory.dart	71.42% <ø> (ø)
...id_redundant_async/avoid_redundant_async_rule.dart	100.00% <100.00%> (ø)
...ules/rules_list/avoid_redundant_async/visitor.dart	100.00% <100.00%> (ø)

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[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
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