Handle invalid IIS log timestamps

[PrzemyslawKlys]

Summary

• Guard against malformed or missing date and time fields by using DateTime.TryParseExact
• Add test data and unit tests for malformed and missing timestamps

Testing

• dotnet test

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https://chatgpt.com/codex/tasks/task_e_68a96ac2566c832eb117ad357f0e459a

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.21%. Comparing base (2059bdb) to head (fb70203).

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #15      +/-   ##
==========================================
+ Coverage   85.82%   87.21%   +1.39%     
==========================================
  Files           3        3              
  Lines         127      133       +6     
  Branches       20       22       +2     
==========================================
+ Hits          109      116       +7     
  Misses         14       14              
+ Partials        4        3       -1     

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