test: stabilize background-run log scenario

[jongalloway]

Summary

Fixes the Ubuntu release-scenarios CI failure by replacing a fixed sleep in the background-run logs scenario with polling for the expected log fragments.

Problem

The release-scenarios workflow failed in Scenario_BackgroundRun_RetrieveLogs_Success because the test assumed the background process would emit all expected log lines within 2 seconds. On slower CI runners, the process startup and log capture can take longer.

Change

• add a helper that polls dotnet_project Logs until the expected stdout and stderr fragments are present or a timeout is reached
• use that helper in Scenario_BackgroundRun_RetrieveLogs_Success instead of a fixed Task.Delay(2000)

Validation

• dotnet build DotNetMcp.slnx --configuration Release
• DOTNET_MCP_SCENARIO_TESTS=1 dotnet test --project DotNetMcp.Tests/DotNetMcp.Tests.csproj --no-build --configuration Release --verbosity normal -- --filter-method *Scenario_BackgroundRun_RetrieveLogs_Success
• DOTNET_MCP_SCENARIO_TESTS=1 dotnet test --project DotNetMcp.Tests/DotNetMcp.Tests.csproj --no-build --configuration Release --verbosity normal -- --filter-namespace DotNetMcp.Tests.Scenarios

Related CI run: https://github.com/jongalloway/dotnet-mcp/actions/runs/23210332665/job/67457113307#step:8:33