Technology refresh: update dependencies and target frameworks

[tillig]

Summary

• Update Autofac from 6.0.0 to 9.1.0
• Update Castle.Core from 4.4.1 to 5.2.1 (major version upgrade)
• Add net10.0 and net8.0 target frameworks
• Update Microsoft.CodeAnalysis.Analyzers to 3.3.4
• Update Microsoft.CodeAnalysis.NetAnalyzers to 9.0.0
• Update Microsoft.SourceLink.GitHub to 10.0.300
• Update StyleCop.Analyzers to 1.2.0-beta.556
• Bump version to 7.0.0 for major dependency updates
• Fix nullability warnings for newer target frameworks

Compatibility Notes

Castle.Core 5.x maintains API compatibility with the Castle.DynamicProxy APIs used in this library. No breaking API changes were required.

Test Results

All 31 tests pass successfully with the updated dependencies.

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 96.39%. Comparing base (283c325) to head (c27b8c1).
⚠️ Report is 5 commits behind head on develop.

Files with missing lines	Patch %	Lines
...ac.Extras.AggregateService/ResolvingInterceptor.cs	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #21      +/-   ##
===========================================
- Coverage    98.18%   96.39%   -1.79%     
===========================================
  Files            4        4              
  Lines          110      111       +1     
  Branches        18       20       +2     
===========================================
- Hits           108      107       -1     
  Misses           1        1              
- Partials         1        3       +2     

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