Kernel: Mark Thread::Blocker leaf subclasses final

Kernel/Net/Routing.cpp

@@ -18,7 +18,7 @@ namespace Kernel {
 
 static Singleton<MutexProtected<HashMap<IPv4Address, MACAddress>>> s_arp_table;
 
-class ARPTableBlocker : public Thread::Blocker {
+class ARPTableBlocker final : public Thread::Blocker {
 public:
     ARPTableBlocker(IPv4Address ip_addr, Optional<MACAddress>& addr);
 

Kernel/Thread.h

@@ -525,7 +525,7 @@ public:
         bool m_should_block { true };
     };
 
-    class QueueBlocker : public Blocker {
+    class QueueBlocker final : public Blocker {
     public:
         explicit QueueBlocker(WaitQueue&, StringView block_reason = {});
         virtual ~QueueBlocker();
@@ -547,7 +547,7 @@ public:
         bool m_did_unblock { false };
     };
 
-    class FutexBlocker : public Blocker {
+    class FutexBlocker final : public Blocker {
     public:
         explicit FutexBlocker(FutexQueue&, u32);
         virtual ~FutexBlocker();