src: mark realm leaf classes final

Since these classes use virtual methods extensively, adding `final`
should allow compilers to optimize accesses better.

PR-URL: #59355
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: Juan José Arboleda <soyjuanarbol@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>

Author: addaleax

src/node_realm.h

@@ -209,7 +209,7 @@ class Realm : public MemoryRetainer {
   CppgcWrapperList cppgc_wrapper_list_;
 };
 
-class PrincipalRealm : public Realm {
+class PrincipalRealm final : public Realm {
  public:
   PrincipalRealm(Environment* env,
                  v8::Local<v8::Context> context,

src/node_shadow_realm.h

@@ -9,7 +9,7 @@
 namespace node {
 namespace shadow_realm {
 
-class ShadowRealm : public Realm {
+class ShadowRealm final : public Realm {
  public:
   static ShadowRealm* New(Environment* env);