[mle] simplify router/leader role restoration upon reset (#10798)

This commit introduces the `RouterRoleRestorer` class, nested within
`MleRouter`, to manage router/leader role restoration after an MLE
operation restart (e.g., a device reboot) by sending multicast Link
Requests. This class simplifies the code and centralizes role
restoration logic.

Specific changes:

- A new member variable `mLastSavedRole` is added to track the last
  attached role (saved in non-volatile memory). This is used by
  `RouterRoleRestorer` to determine the number of Link Request
  attempts. This variable replaces the previous `mWasLeader`, which
  was only updated after a reboot and would not account for role
  changes afterward.
- The `AttachTimer` is now used for role restoration instead of the
  retransmission timer, as role restoration always occurs while the
  device is detached and before any attach attempts.
- The `kLinkRequestTimeout` is used for the last attempt before
  considering restoration failure.
- The `mChallengeTimeout` mechanism is now removed (in earlier Thread
  specification versions, multicast Link Requests could be used while
  the device was attached, but this is no longer used or needed).
- `test-012-reset-recovery.py` is updated to validate the role
  restoration behavior. `test_detach` is also updated and fixed.

tests/scripts/thread-cert/border_router/test_publish_meshcop_service.py

@@ -133,8 +133,7 @@ class PublishMeshCopService(thread_cert.TestCase):
         br1.stop()
         br1.set_active_dataset(updateExisting=True, network_name='ot-br1-1')
         br1.start()
-        self.simulator.go(config.BORDER_ROUTER_STARTUP_DELAY)
-        self.simulator.go(5)  # Needs to wait extra some time to update meshcop service on state changes.
+        self.simulator.go(config.LEADER_REBOOT_DELAY)
         self.check_meshcop_service(br1, host)
 
         # verify that there are two meshcop services
@@ -142,7 +141,7 @@ class PublishMeshCopService(thread_cert.TestCase):
         br2.start()
         br2.disable_backbone_router()
         br2.enable_br()
-        self.simulator.go(config.BORDER_ROUTER_STARTUP_DELAY)
+        self.simulator.go(config.LEADER_REBOOT_DELAY)
 
         service_instances = host.browse_mdns_services('_meshcop._udp')
         self.assertEqual(len(service_instances), 2)

tests/scripts/thread-cert/config.py

@@ -138,6 +138,7 @@ SECURITY_POLICY = [672, 'onrc']
 
 LEADER_STARTUP_DELAY = 12
 ROUTER_STARTUP_DELAY = 10
+LEADER_REBOOT_DELAY = 40
 ED_STARTUP_DELAY = 5
 BORDER_ROUTER_STARTUP_DELAY = 20
 MAX_NEIGHBOR_AGE = 100

tests/scripts/thread-cert/test_detach.py

@@ -145,10 +145,9 @@ class TestDetach(thread_cert.TestCase):
         self.assertEqual(leader.get_state(), 'disabled')
 
         leader.start()
-        # leader didn't become leader after the last start(), so it re-syncs in a non-critical manner thus taking ROUTER_RESET_DELAY to recover
-        self.simulator.go(config.ROUTER_RESET_DELAY / 2)
+        self.simulator.go(config.LEADER_RESET_DELAY / 2)
         self.assertEqual(leader.get_state(), 'detached')
-        self.simulator.go(config.ROUTER_RESET_DELAY / 2)
+        self.simulator.go(config.LEADER_RESET_DELAY / 2)
         self.assertEqual(leader.get_state(), 'leader')
         router1.start()
         self.simulator.go(config.ROUTER_RESET_DELAY)