ITSMFTTracking: add Gate 4 B3.1 ownership/reset/transactional-load acceptance tests

New testGate4B31OwnershipContract.cxx, covering the acceptance criteria the
TimeFrame/LegacyTrackerScratch<NLayers> split's design requires and that
were not already incidental coverage elsewhere:

1. resetScratch() clears scratch-owned state only; a populated TimeFrame's
   CommonTracks/vertices survive untouched.
2. resetTimeFrameEvent() -- the helper ITSMFTTrackingInterface<NLayers>::
   resetEvent() trivially wraps -- clears both owners.
3. Two scratches (<7>, <10>) bound to one shared TimeFrame: resetting one
   never touches the other scratch or the shared frame.
4. An allocation failure injected into the scratch-side legacy backfill
   staging, after the TimeFrame-side normalized decode has already
   succeeded, leaves both live owners exactly at their pre-load state.
5. Compile-time proof (static_assert) that TimeFrame is the plain,
   non-templated owner this slice introduced, not a surviving
   TimeFrame<NLayers> template.
6. mPropagatorDevice, relocated unchanged onto TimeFrame, remains inert
   through the base class's own getDevicePropagator()/
   setDevicePropagator() hooks.

Registered as gate4-b31-ownership-contract in test/CMakeLists.txt.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: mpuccio

Detectors/ITSMFT/common/tracking/test/CMakeLists.txt

@@ -257,6 +257,12 @@ o2_add_test(timeframe-covariance-lifecycle
             LABELS "itsmft;tracking"
             PUBLIC_LINK_LIBRARIES O2::ITSMFTTracking O2::MFTTracking)
 
+o2_add_test(gate4-b31-ownership-contract
+            SOURCES testGate4B31OwnershipContract.cxx
+            COMPONENT_NAME itsmft-tracking
+            LABELS "itsmft;tracking"
+            PUBLIC_LINK_LIBRARIES O2::ITSMFTTracking O2::MFTTracking O2::DetectorsBase)
+
 o2_add_test(catracker-failure-contract
             SOURCES testCATrackerFailureContract.cxx
             COMPONENT_NAME itsmft-tracking