[mlr] introduce state machine and use timer in Mlr::Manager (openthread#13132)

This commit introduces a structured state machine to `Mlr::Manager` to
coordinate Multicast Listener Registration (MLR) activities more
efficiently. The previous implementation relied on independent delay
variables and the global `TimeTicker`, which could lead to redundant
or premature registrations, especially when a Primary Backbone Router
(PBBR) was newly discovered or updated.

The new state machine (`kStateStopped`, `kStateIdle`,
`kStateToRegisterAll`, `kStateRegistering`, `kStateRegistered`,
`kStateNewAddrToRegister`) provides explicit transitions for the
entire MLR lifecycle. This ensures that registrations are properly
aggregated and that periodic renewals are correctly rescheduled after
successful out-of-band registrations.

Additionally, the manager now uses a dedicated `TimerMilli` instead of
`TimeTicker`, reducing system-wide overhead and providing more
precise timing control.

Author: abtink

src/core/common/time_ticker.cpp

@@ -111,13 +111,6 @@ void TimeTicker::HandleTimer(void)
     }
 #endif
 
-#if OPENTHREAD_CONFIG_MLR_ENABLE || (OPENTHREAD_FTD && OPENTHREAD_CONFIG_TMF_PROXY_MLR_ENABLE)
-    if (mReceivers & Mask(kMlrManager))
-    {
-        Get<Mlr::Manager>().HandleTimeTick();
-    }
-#endif
-
     if (mReceivers & Mask(kIp6Mpl))
     {
         Get<Ip6::Mpl>().HandleTimeTick();

src/core/common/time_ticker.hpp

@@ -67,7 +67,6 @@ class TimeTicker : public InstanceLocator, private NonCopyable
         kChildSupervisor,        ///< `ChildSupervisor`
         kIp6FragmentReassembler, ///< `Ip6::Ip6` (handling of fragmented messages)
         kDuaManager,             ///< `DuaManager`
-        kMlrManager,             ///< `MlrManager`
         kNetworkDataNotifier,    ///< `NetworkData::Notifier`
         kIp6Mpl,                 ///< `Ip6::Mpl`
         kBbrLocal,               ///< `BackboneRouter::Local`