HttpClient default and per request timeout: retarget net10.0, add timeout-vs-cancellation and resilience samples

[vladimir-pecanac-main]

Sample update for "Change Default and per Request Timeout in HttpClient" (code-maze.com/aspnetcore-change-default-and-per-request-timeout-in-httpclient/). This PR touches only aspnetcore-features/HttpClientDefaultAndPerRequestTimeOut.

Changes:

• Both projects retargeted from net8.0 to net10.0. The web project now has Nullable enabled (no new warnings).
• Test packages: Microsoft.NET.Test.Sdk 17.8.0 to 18.10.1, xunit 2.5.3 to 2.9.3, xunit.runner.visualstudio 2.5.3 to 4.0.0, coverlet.collector 6.0.0 to 10.0.1, Microsoft.AspNetCore.Mvc.Testing 8.0.4 to 10.0.12.
• Web project: Microsoft.Extensions.Http.Resilience 10.10.0 added. A second named client, ResilientClient, is registered with AddStandardResilienceHandler (2 second attempt timeout, 8 second total timeout), and /api/test-resilience-timeout reports the exception type and the client's Timeout after the call fails.
• New /api/test-timeout-vs-cancellation endpoint that separates a timeout from a caller cancellation with catch (OperationCanceledException ex) when (ex.InnerException is TimeoutException).
• Two new tests for the two endpoints, added to EndpointsLiveTests, so the CI filter FullyQualifiedName!~Live keeps skipping them like the existing four. They need port 5000 free and real wall-clock timeouts.
• Removed template residue: the Microsoft.VisualStudio.Azure.Containers.Tools.Targets package with DockerDefaultTargetOS and DockerfileContext (the folder has no Dockerfile), AddControllers, MapControllers, UseAuthorization and UseHttpsRedirection (no controllers, no authorization, and the app listens on plain http://localhost:5000), and four using directives that ImplicitUsings already covers.
• The three HttpResponseMessage locals are now declared with using var so they are disposed.

Package versions were re-queried on NuGet on 2026-09-23. Microsoft.NET.Test.Sdk is 18.10.1 today, one patch above the 18.10.0 the batch plan named, so 18.10.1 is what this PR uses. xunit 2.9.3, xunit.runner.visualstudio 4.0.0, coverlet.collector 10.0.1, Microsoft.AspNetCore.Mvc.Testing 10.0.12 and Microsoft.Extensions.Http.Resilience 10.10.0 match the plan.

Verified locally on SDK 10.0.302, runtime Microsoft.NETCore.App 10.0.10: dotnet build -c Release with 0 warnings and 0 errors, dotnet test with 6 of 6 passing when the Live tests are run directly, dotnet test --filter "FullyQualifiedName!~Live" exits 0 with no test selected (what CI runs), and dotnet list package --vulnerable --include-transitive clean on both projects. launchSettings.json is unchanged.