fix(test): disable memory monitor in cross-kernel snapshot restore test

MemoryMonitor's is_guest_mem heuristic matches a single guest-sized VMA,
but _test_balloon inflates the balloon after restore, and
GuestRegionMmapExt::discard_range overlays MAP_FIXED anonymous mmaps on
the reclaimed ranges (a workaround specific to private file-backed
mappings from snapshot restore). This fragments the 512 MiB guest VMA
into ~190 smaller ones, none of which match the heuristic, and their RSS
(~336 MiB) is counted as VMM overhead.

This is the only cross-kernel test that inflates the balloon post-
restore, and its purpose is validating cross-kernel compatibility, not
VMM memory overhead, so the monitor is skipped here as it already is in
test_snapshot_phase1.

Signed-off-by: Jack Thomson <jackabt@amazon.com>

Author: JackThomson2

tests/integration_tests/functional/test_snapshot_restore_cross_kernel.py

@@ -115,7 +115,11 @@ def test_snap_restore_from_artifacts(
     # in the snapshot root dir.
     logger.info("Working with snapshot artifacts in %s.", snapshot_dir)
 
-    vm = microvm_factory.build()
+    # Skip memory monitor: the balloon inflation below fragments the guest
+    # VMA via discard_range's MAP_FIXED anonymous mmap workaround (used only
+    # for private file-backed mappings from snapshot restore), defeating
+    # MemoryMonitor.is_guest_mem. Cross-kernel test, not overhead.
+    vm = microvm_factory.build(monitor_memory=False)
     vm.time_api_requests = False
     vm.spawn()
     logger.info("Loading microVM from snapshot...")