test(raft-drive-async): network-partition soak primitive + RED/GREEN scenario (task 4.1)

Add in-process partition blackhole primitive (no privilege required):
- Evict partitioned peer from standby_endpoints so reconnect fires
- RED mode: reconnect connect parks in gate → blocks delaymgr tick
  (proves pre-change build heartbeat stalls on unreachable peer)
- GREEN mode: real offload path runs → slowlane_submit non-blocking
  → tick returns promptly → survivor heartbeats continue every tick
- Heal: re-add peer, both standbys receive heartbeats post-heal

Requirements: 7.1, 7.2, 7.3, 7.4
Boundary: PartitionTest

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

src/controller/testsuite/controller_test.c

@@ -72,6 +72,8 @@ extern void test_commit_admission_pool(void);
 extern void test_ha_vep_teardown(void);
 extern void test_ha_dispatch_integration(void);
 extern void test_ha_core_safety(void);
+extern void test_ha_partition(void);
+extern void test_ha_partition(void);
 
 void setUp(void) { return; }
 
@@ -213,6 +215,7 @@ int main(int argc, char* argv[])
     TEST(test_ha_vep_teardown);
     TEST(test_ha_dispatch_integration);
     TEST(test_ha_core_safety);
+    TEST(test_ha_partition);
 
     return UNITY_END();
 }