Add .NET 10.0 target framework support

[Copilot]

Adds net10.0 TFM across the repository. Updates global.json SDK version, adds net10.0 to library multi-targeting, makes it the primary TFM for sample apps, and configures GitHub Actions to test on net10.0.

Changes

Core libraries - Added net10.0 to multi-target frameworks:

• Fluid.csproj: netstandard2.0;net8.0;net9.0;net10.0
• Fluid.ViewEngine.csproj: netstandard2.0;net8.0;net9.0;net10.0
• Fluid.MvcViewEngine.csproj: net8.0;net9.0;net10.0 (includes ASP.NET Core 10.0.0 FrameworkReference)
• MinimalApis.LiquidViews.csproj: net8.0;net9.0;net10.0

Test project - Added net10.0:

• Fluid.Tests.csproj: Tests now run on net8.0;net9.0;net10.0

Sample apps & benchmarks - Changed from net9.0 to net10.0:

• Fluid.MinimalApisSample.csproj
• Fluid.MvcSample.csproj
• Fluid.Benchmarks.csproj

Build configuration:

• global.json: SDK version 9.0.100 → 10.0.100
• GitHub Actions workflows: Added 10.0.x to dotnet-version matrix

Note: .NET 10.0 SDK not yet released; changes follow established TFM conventions.

Original prompt

Add thet net10.0 tfm to the list of targets. Make it the main TFM for sample applications. Update or add tht global.json. Run tests on net10.0 too in github actions.

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