Update dependencies while respecting .NET version constraints

[Copilot]

Summary

This PR updates all outdated NuGet package dependencies in the OAT project to their latest compatible versions while respecting .NET target framework version constraints. The key principle followed is that packages targeting specific .NET versions (e.g., net8.0) are not upgraded across major framework versions (e.g., 8.x to 9.x).

Changes

Framework-Independent Packages

Updated across all target frameworks to their latest stable versions:

• Nerdbank.GitVersioning: 3.7.115 → 3.8.118
• Microsoft.NET.Test.Sdk: 17.14.1 → 18.0.0
• xunit.runner.visualstudio: 3.1.4 → 3.1.5
• System.Collections.Immutable: 9.0.9 → 9.0.10
• System.Net.Http.Json: 9.0.9 → 9.0.10

.NET 8.0 Specific Packages

Updated to the latest 8.x versions (did not cross into 9.x major versions):

• Microsoft.AspNetCore.Components: 8.0.20 → 8.0.21
• Microsoft.AspNetCore.Components.Web: 8.0.20 → 8.0.21
• Microsoft.AspNetCore.Components.WebAssembly: 8.0.19 → 8.0.21
• Microsoft.AspNetCore.Components.WebAssembly.DevServer: 8.0.19 → 8.0.21

.NET 9.0 Specific Packages

Updated to the latest 9.x versions:

• Microsoft.AspNetCore.Components: 9.0.9 → 9.0.10
• Microsoft.AspNetCore.Components.Web: 9.0.9 → 9.0.10

Modified Files

• Directory.Build.props
• OAT/OAT.csproj
• OAT.Tests/OAT.Tests.csproj
• OAT.Blazor/OAT.Blazor.csproj
• OAT.Blazor.Components/OAT.Blazor.Components.csproj

Verification

• ✅ All projects build successfully
• ✅ All 66 tests pass on both net8.0 and net9.0 target frameworks
• ✅ No new warnings introduced
• ✅ No security vulnerabilities detected in updated dependencies
• ✅ Backward compatibility maintained by respecting major version boundaries

Notes

The OAT.Blazor.Components project uses conditional package references to ensure that net8.0 targets receive 8.x versions of ASP.NET Core packages, while net9.0 targets receive 9.x versions. This pattern has been preserved and properly updated in this PR.

Original prompt

Update dependencies in the OAT project. When dependencies are defined in the csproj as being targeted to a specific version of .NET, don't upgrade them across major versions (i.e. 8 to 9).

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