fix(ci): align all projects on net9.0, upgrade actions to v5, enable VM tests

- Change test projects from net10.0 to net9.0 to match source projects
- Update build workflow from net8.0 to net9.0
- Upgrade checkout to v5, setup-dotnet to v5 across all workflows
- Remove outdated PS 7.2 test matrix entries
- Restructure integration tests: create test keeps VM alive so start/stop,
  snapshot, and cloud-init tests can use it instead of skipping. AfterAll
  handles cleanup.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/integration-tests.yml

@@ -48,7 +48,7 @@ jobs:
     timeout-minutes: 45
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
 
       # ── Pre-flight cleanup ─────────────────────────────────────────────
 
@@ -217,7 +217,7 @@ jobs:
 
       - name: Upload test results
         if: always()
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v5
         with:
           name: integration-test-results
           path: TestResults/