chore: remove strong-mode from analysis_options since it is no longer supported

[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:

Reference: dart-lang/sdk#50751

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[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: 537

• Total lines of source code: 9466

• Total classes: 404

• Average Cyclomatic Number per line of code: 0.37 / 2

• Average Source Lines of Code per method: 6

• Total tech debt: 1984.0 hours

• Found issues: 5 ⚠

[codecov]

Codecov Report

Merging #1107 (d1173fc) into master (ce31833) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1107   +/-   ##
=======================================
  Coverage   85.02%   85.02%           
=======================================
  Files         339      339           
  Lines        7445     7445           
=======================================
  Hits         6330     6330           
  Misses       1115     1115           

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