perf(ffi/v8): inline Value storage to eliminate heap allocation per primitive

The Value type previously used std::shared_ptr<ValueStorage> for every
value, causing a heap allocation + atomic ref count on every Value
creation. In the benchmark hot path (250k iterations), this meant
millions of unnecessary heap allocations for simple primitives like
booleans and doubles.

Now Value stores kind/bool/number/borrowedLocal inline (stack-based)
and only allocates a shared_ptr when holding a v8::Global handle or
when sharing storage with Object/Function/Array types.

This eliminates heap allocation for:
- Value() (undefined)
- Value(bool)
- Value(double/int)
- Value::null()
- Value::borrowed(runtime, local)

Tests: macOS v8 713/0

Author: DjDeveloperr

NativeScript/ffi/v8/NativeApiV8Runtime.h

@@ -126,7 +126,7 @@ struct RuntimeState {
 };
 
 struct ValueStorage {
-  enum class Kind {
+  enum class Kind : uint8_t {
     Undefined,
     Null,
     Bool,
@@ -279,34 +279,37 @@ class String {
 
 class Value {
  public:
-  Value()
-      : storage_(
-            std::make_shared<v8engine::ValueStorage>(v8engine::ValueStorage::Kind::Undefined)) {}
+  Value() : kind_(v8engine::ValueStorage::Kind::Undefined) {}
 
-  Value(bool value)
-      : storage_(std::make_shared<v8engine::ValueStorage>(v8engine::ValueStorage::Kind::Bool)) {
-    storage_->boolValue = value;
-  }
+  Value(bool value) : kind_(v8engine::ValueStorage::Kind::Bool), boolValue_(value) {}
 
-  Value(double value)
-      : storage_(std::make_shared<v8engine::ValueStorage>(v8engine::ValueStorage::Kind::Number)) {
-    storage_->numberValue = value;
-  }
+  Value(double value) : kind_(v8engine::ValueStorage::Kind::Number), numberValue_(value) {}
 
   Value(int value) : Value(static_cast<double>(value)) {}
   Value(uint32_t value) : Value(static_cast<double>(value)) {}
 
   Value(Runtime& runtime, const Value& value) {
-    if (value.storage_->kind == v8engine::ValueStorage::Kind::V8Borrowed) {
+    if (value.kind_ == v8engine::ValueStorage::Kind::V8Borrowed) {
+      // Promote borrowed to owned
       storage_ =
           std::make_shared<v8engine::ValueStorage>(v8engine::ValueStorage::Kind::V8);
-      storage_->value.Reset(runtime.isolate(), value.storage_->borrowedValue);
+      storage_->value.Reset(runtime.isolate(), value.borrowedValue_);
+      kind_ = v8engine::ValueStorage::Kind::V8;
       return;
     }
+    kind_ = value.kind_;
+    boolValue_ = value.boolValue_;
+    numberValue_ = value.numberValue_;
+    borrowedValue_ = value.borrowedValue_;
     storage_ = value.storage_;
   }
-  Value(Runtime& runtime, Value&& value) : storage_(std::move(value.storage_)) {}
-  Value(Runtime& runtime, const String& value) : storage_(value.storage_) {}
+  Value(Runtime& runtime, Value&& value)
+      : kind_(value.kind_),
+        boolValue_(value.boolValue_),
+        numberValue_(value.numberValue_),
+        borrowedValue_(value.borrowedValue_),
+        storage_(std::move(value.storage_)) {}
+  Value(Runtime& runtime, const String& value);
   Value(Runtime& runtime, const Object& object);
   Value(Runtime& runtime, const Function& function);
   Value(Runtime& runtime, const Array& array);
@@ -317,7 +320,7 @@ class Value {
 
   static Value null() {
     Value value;
-    value.storage_ = std::make_shared<v8engine::ValueStorage>(v8engine::ValueStorage::Kind::Null);
+    value.kind_ = v8engine::ValueStorage::Kind::Null;
     return value;
   }
 
@@ -339,34 +342,48 @@ class Value {
 
   v8::Local<v8::Value> local(Runtime& runtime) const {
     v8::Isolate* isolate = runtime.isolate();
-    switch (storage_->kind) {
+    switch (kind_) {
       case v8engine::ValueStorage::Kind::Undefined:
         return v8::Undefined(isolate);
       case v8engine::ValueStorage::Kind::Null:
         return v8::Null(isolate);
       case v8engine::ValueStorage::Kind::Bool:
-        return v8::Boolean::New(isolate, storage_->boolValue);
+        return v8::Boolean::New(isolate, boolValue_);
       case v8engine::ValueStorage::Kind::Number:
-        return v8::Number::New(isolate, storage_->numberValue);
+        return v8::Number::New(isolate, numberValue_);
       case v8engine::ValueStorage::Kind::V8:
         return storage_->value.Get(isolate);
       case v8engine::ValueStorage::Kind::V8Borrowed:
-        return storage_->borrowedValue;
+        return borrowedValue_;
     }
   }
 
   Value(Runtime& runtime, v8::Local<v8::Value> value)
-      : storage_(std::make_shared<v8engine::ValueStorage>(v8engine::ValueStorage::Kind::V8)) {
+      : kind_(v8engine::ValueStorage::Kind::V8),
+        storage_(std::make_shared<v8engine::ValueStorage>(v8engine::ValueStorage::Kind::V8)) {
     storage_->value.Reset(runtime.isolate(), value);
   }
 
   static Value borrowed(Runtime&, v8::Local<v8::Value> value) {
     Value result;
-    result.storage_->kind = v8engine::ValueStorage::Kind::V8Borrowed;
-    result.storage_->borrowedValue = value;
+    result.kind_ = v8engine::ValueStorage::Kind::V8Borrowed;
+    result.borrowedValue_ = value;
     return result;
   }
 
+  // Access the shared storage (for Object/Function/Array interop)
+  std::shared_ptr<v8engine::ValueStorage> storage() const { return storage_; }
+
+  static Value fromStorage(std::shared_ptr<v8engine::ValueStorage> s) {
+    Value v;
+    v.kind_ = s->kind;
+    v.boolValue_ = s->boolValue;
+    v.numberValue_ = s->numberValue;
+    v.borrowedValue_ = s->borrowedValue;
+    v.storage_ = std::move(s);
+    return v;
+  }
+
  private:
   friend class Runtime;
   friend class Object;
@@ -376,6 +393,10 @@ class Value {
   friend class Function;
   friend class Array;
 
+  v8engine::ValueStorage::Kind kind_ = v8engine::ValueStorage::Kind::Undefined;
+  bool boolValue_ = false;
+  double numberValue_ = 0;
+  v8::Local<v8::Value> borrowedValue_;
   std::shared_ptr<v8engine::ValueStorage> storage_;
 };
 
@@ -506,9 +527,7 @@ class Object {
   }
 
   operator Value() const {
-    Value value;
-    value.storage_ = storage_;
-    return value;
+    return Value::fromStorage(storage_);
   }
 
  protected:
@@ -631,9 +650,7 @@ class Function : public Object {
   }
 
   operator Value() const {
-    Value value;
-    value.storage_ = storage_;
-    return value;
+    return Value::fromStorage(storage_);
   }
 };
 
@@ -672,9 +689,7 @@ class Array : public Object {
   }
 
   operator Value() const {
-    Value value;
-    value.storage_ = storage_;
-    return value;
+    return Value::fromStorage(storage_);
   }
 };
 
@@ -709,9 +724,7 @@ class BigInt {
   }
 
   operator Value() const {
-    Value value;
-    value.storage_ = storage_;
-    return value;
+    return Value::fromStorage(storage_);
   }
 
  private:
@@ -748,9 +761,7 @@ class ArrayBuffer : public Object {
   }
 
   operator Value() const {
-    Value value;
-    value.storage_ = storage_;
-    return value;
+    return Value::fromStorage(storage_);
   }
 };
 }  // namespace engine