Support open-generic notification handlers with full scenario tests

[Copilot]

Summary

• added robust open-generic registration in notification service registration so INotificationHandler<> handlers can be resolved for concrete notifications
• kept compatibility with existing concrete notification handlers
• added integration tests for all target scenarios:
  • Publish<T> invokes both specific and open-generic handlers
  • Publish(object) invokes both specific and open-generic handlers
  • open-generic handler still runs when no specific handler exists
• added unit test to verify open-generic notification handler registration in DI

Validation

• dotnet test tests/DispatchR.UnitTest/DispatchR.UnitTest.csproj --nologo
• dotnet test tests/DispatchR.IntegrationTest/DispatchR.IntegrationTest.csproj --nologo
• coverage run (merged Unit + Integration for DispatchR module):
  • Line: 100%
  • Branch: 98.36%
  • Method: 100%

Notes

• one final parallel_validation rerun could not execute due validation time budget exhaustion, but earlier run passed CodeQL and review feedback was addressed.

[codecov]

Codecov Report

❌ Patch coverage is 90.90909% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/DispatchR/Configuration/ServiceRegistrator.cs	90.90%	0 Missing and 2 partials ⚠️

📢 Thoughts on this report? Let us know!