Target PowerShell host to .NET 10

[eosfor]

Summary

Follow-up after #48.

Moves the local/F5 Verso host path to .NET 10 while keeping the Verso.PowerShell package compatible with both runtime lines.

Changes

• Target Verso.Host and Verso.Host.Tests to net10.0.
• Multi-target Verso.PowerShell for net8.0 and net10.0.
• Use TFM-specific PowerShell SDK versions:
  • net8.0 -> Microsoft.PowerShell.SDK 7.4.15
  • net10.0 -> Microsoft.PowerShell.SDK 7.6.1
• Use TFM-specific Roslyn versions to avoid dependency conflicts with PowerShell SDK 7.6.x.
• Publish the VS Code bundled host explicitly with -f net10.0.
• Prefer net10 host discovery in VS Code development mode, with net8 fallback.

Base

#48 is merged. This branch has been rebuilt on current main, so the PR now contains only the .NET 10 follow-up changes.

Validation

• dotnet test tests/Verso.PowerShell.Tests/Verso.PowerShell.Tests.csproj -c Debug --no-restore
• dotnet test tests/Verso.Host.Tests/Verso.Host.Tests.csproj -c Debug --no-restore
• npm run lint
• npm run pretest