feat(logging): thread safety with ConcurrentDictionary for scope storage

[hjgraca]

Please provide the issue number

Issue number: #1076

Summary

Changes

• Replace inner Dictionary with ConcurrentDictionary in _threadScopes to ensure thread-safe operations on scope values
• Update Scope property return type from IDictionary to ConcurrentDictionary for consistency
• Refactor SetKey method to use intermediate variable for better readability and null handling
• Replace manual ContainsKey/Remove checks with TryRemove for atomic operations in RemoveKeys and RemoveKey methods
• Update GetAllKeys to return a snapshot via ToArray() to prevent concurrent modification exceptions during enumeration
• Add documentation clarifying that inner dictionary is ConcurrentDictionary and that GetAllKeys returns a snapshot for thread-safety
• Improve code consistency by using ConcurrentDictionary methods throughout instead of mixing Dictionary and ConcurrentDictionary patterns

User experience

Please share what the user experience looks like before and after this change

Checklist

Please leave checklist items unchecked if they do not apply to your change.

• Meets tenets criteria
• I have performed a self-review of this change
• Changes have been tested
• Changes are documented
• PR title follows conventional commit semantics

Is this a breaking change?

RFC issue number:

Checklist:

• Migration process documented
• Implement warnings (if it can live side by side)

Acknowledgment

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 78.50%. Comparing base (1a1a3fa) to head (38e8bad).
⚠️ Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
.../src/AWS.Lambda.Powertools.Logging/Logger.Scope.cs	85.71%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1099      +/-   ##
===========================================
- Coverage    78.55%   78.50%   -0.06%     
===========================================
  Files          299      299              
  Lines        12376    12375       -1     
  Branches      1494     1492       -2     
===========================================
- Hits          9722     9715       -7     
- Misses        2180     2186       +6     
  Partials       474      474              

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