Upgrade to .NET 10.0 (drop .NET 9.x support)

[Copilot]

Major version upgrade targeting .NET 10.0 exclusively. Removes backward compatibility with .NET 9.x and earlier.

Core Changes

• Target Framework: net9.0 → net10.0 in all projects
• Version: 9.2.2 → 10.0.0 (major bump for breaking change)
• Dependencies:
  • Microsoft.Extensions.*: 9.0.10 → 10.0.0
  • xunit.v3*: 3.1.0 → 3.2.0
  • Microsoft.NET.Test.Sdk: 18.0.0 → 18.0.1

Build Infrastructure

• Azure Pipelines: Updated both PR and release pipelines to use .NET SDK 10.0.100
• Version Variables: Updated Major/Minor/Revision to 10.0.0

Code Fixes

• Fixed C# keyword conflict: renamed lambda parameter scoped → scopedSvc in test code (C# 11+ reserved keyword)

Documentation

• Updated README.md with .NET 10.0 requirements
• Created CHANGELOG.md with migration guidance

Migration Path

Projects consuming this library must:

1. Upgrade to .NET 10.0 SDK
2. Update TargetFramework to net10.0
3. Update package reference to 10.0.0+

All 43 tests pass. NuGet package generates correctly with lib/net10.0/ target.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Support .NET SDK 10</issue_title>
<issue_description>Plan and Actions:

To fully upgrade to .NET SDK 10 (dropping backward compatibility):

1. Update all .csproj files to target net10.0 only
   • Remove any references to previous TargetFrameworks/TFMs (net8.0, net6.0, etc.)
   • Ensure all projects and test projects target ONLY net10.0
   • Increment the version number to 10.0.0 in Xunit.Microsoft.DependencyInjection.csproj found in here: <Version Condition="'$(Version)' == ''">9.2.2</Version>
2. Upgrade NuGet package dependencies
   • Use dotnet list package --outdated to identify packages requiring updates
   • Upgrade each package to the latest compatible version for .NET 10 using NuGet
   • Fix code as needed for any breaking changes introduced by new dependencies
   • Validate all code builds and runs with updated dependencies
3. Update build pipelines (GitHub Actions if any)
   • Modify workflow files to use actions/setup-dotnet with SDK 10 (10.x)
   • Remove matrix entries for older SDK versions
   • Validate pipeline, both PR and release, builds and tests with SDK 10 only
   • The build pipelines are the following yml files only:
     • azure-pipeline-PR.yml
     • azure-pipelines.yml - Increment the major number to 10, minor and revision to both 0 in this yml file
4. Run and fix all tests
   • Ensure the entire test suite passes on net10.0
   • Address any failures due to upgraded dependencies or SDK changes
5. Documentation and release
   • Update README, changelog, and documentation to specify .NET 10 minimum requirement
   • Set appropriate version bump (major if public APIs or support dropped)
   • Do not publish to NuGet as it will be a manual process

Deliverables:

• Branch: support/net10 with all changes
• PR: "Support .NET SDK 10 (net10.0 only, no backward compatibility)"
• Changelog entries, CI status, publishing info
• Do not run azure-pipelines.yml as that will be a manual process. Run azure-pipeline-PR.yml only to validate.

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Decision:

• Targeting net10.0 only. All compatibility with previous .NET SDKs is removed.
• No multi-targeting; this is a breaking change for consumers relying on older SDKs.

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Next steps:

• Execute the above in sequence and open a PR for review once ready.

Draft for your approval before implementation.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Support .NET SDK 10 #326

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