Fix NuGet package versioning for release pipeline v9.2.0

[Copilot]

The release pipeline for version 9.2.0 was failing because the project lacked proper NuGet package versioning configuration. The pipeline defines version variables (Major: 9, Minor: 2, Revision: 0) but these weren't being used during package generation, causing packages to be created with the default version 1.0.0 instead of 9.2.0.

Root Cause

The project file was missing essential NuGet package metadata properties, and an obsolete package.nuspec file contained outdated version information. Additionally, the Azure pipeline wasn't passing version parameters to the dotnet pack command.

Changes Made

Updated Xunit.Microsoft.DependencyInjection.csproj:

• Added comprehensive NuGet package metadata including PackageId, Title, Authors, Company, Description, Copyright, PackageTags, PackageProjectUrl, PackageLicenseExpression, and PackageRequireLicenseAcceptance
• Removed dependency on external .nuspec file by moving all metadata into the project file

Removed obsolete package.nuspec:

• Eliminated conflicting version source that was causing versioning issues

Updated azure-pipelines.yml:

• Added /p:PackageVersion=$(Major).$(Minor).$(Revision) parameter to the pack command to properly use pipeline version variables

Verification

The fix has been thoroughly tested:

• Local build and pack operations succeed with correct version 9.2.0
• All 43 example tests continue to pass
• Generated NuGet package contains proper version and complete metadata
• Full pipeline simulation (restore → build → pack → test) executes successfully

The release pipeline should now correctly generate NuGet packages with version 9.2.0 and all required metadata.

Fixes #315.

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.