.NET: Upgrade to .NET 10

[stephentoub]

• Require .NET 10 SDK
• Include net10.0 assets in all assemblies
• Move net9.0-only targets to net10.0
• Update LangVersion to latest
• Remove complicated distinctions between debug target TFMs and release target TFMs
• Remove unnecessary package dependencies when built-in to netcoreapp
• Clean up some ifdefs
• Clean up some analyzer warnings

[Copilot]

Pull Request Overview

This PR upgrades the .NET target framework from .NET 9.0 to .NET 10.0 across the entire codebase. The changes include updating SDK requirements, target frameworks in project files, package versions, and leveraging new C# language features available in .NET 10.0.

Key Changes:

• Updated global SDK requirement to .NET 10.0.100 with minor rollForward policy
• Migrated all projects from net9.0 to net10.0 target framework
• Updated package versions to 10.0.0 where applicable and conditionally included packages only needed for pre-net10.0 frameworks
• Adopted new C# language features including collection expressions, field-backed properties, and simplified syntax

Reviewed Changes

Copilot reviewed 215 out of 215 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
dotnet/global.json	Updated SDK version to 10.0.100 with minor rollForward policy
dotnet/Directory.Build.props	Updated LangVersion to latest and redefined target frameworks for net10.0
dotnet/Directory.Packages.props	Updated Microsoft.AspNetCore packages to 10.0.0
dotnet/tests/Directory.Build.props	Updated default test target frameworks to net10.0;net472
dotnet/samples/Directory.Build.props	Updated sample target frameworks to net10.0;net472
Multiple .csproj files	Removed TargetFrameworks property and updated to net10.0
Multiple .csproj files	Conditionally included System.Net.ServerSentEvents and related packages for pre-net10.0 frameworks
Multiple .cs files	Adopted collection expressions, field-backed properties, and pattern matching improvements
PowerShell scripts	Updated paths from net9.0 to net10.0
Documentation files	Updated .NET version references from 9.0 to 10.0
GitHub workflows	Updated CI/CD workflows to use .NET 10.0

[crickman]

@stephentoub - This is going to create conflicts with the v2 feature branch feature-foundry-agents. I wonder if this can wait until after Ignite, or perhaps just after Agents V2 Public Preview (at which time feature-foundry-agents will be merged to main).

I look forward to the upgrade to net10.0, but I'm just wondering about order of execution here.

[stephentoub]

@stephentoub - This is going to create conflicts with the v2 feature branch feature-foundry-agents. I wonder if this can wait until after Ignite, or perhaps just after Agents V2 Public Preview (at which time feature-foundry-agents will be merged to main).

@crickman, has this happened?

[crickman]

@stephentoub - This is going to create conflicts with the v2 feature branch feature-foundry-agents. I wonder if this can wait until after Ignite, or perhaps just after Agents V2 Public Preview (at which time feature-foundry-agents will be merged to main).

@crickman, has this happened?

Yes, merged this morning.

[crickman]

Looks great, can't wait. I have no doubt you're on top of merging and resolving conflicts. Ping me if you need reapproval.