@brougkr fix(unreal): Replace FTickableGameObject with FTSTicker (#4835)

# Description of Changes
This is a copy of #4006 with only the updates to the way Unreal handles
ticks. As per @brougkr findings:

- **FTickableGameObject initialization order bug** - Replaced with
FTSTicker for reliable tick registration:
  - Removed FTickableGameObject inheritance
  - Added FTSTicker::FDelegateHandle for manual tick registration
  - Added destructor to clean up ticker registration
  - Added OnTickerTick() method

### Issue
FTickableGameObject registers itself in its constructor BEFORE
UDbConnectionBase's constructor body runs. Even with
ETickableTickType::Never, UE's GENERATED_BODY() macro can interfere with
base class initialization order, causing the default constructor to be
called instead.

# API and ABI breaking changes

- Refactor of an underlying component of the SDK and non-breaking.

# Expected complexity level and risk

2 - This changes the structure of how the database tooling can
auto-tick, but is invisible to the developer

# Testing

As this changes a core feature I tested all aspects:
- [x] Reproduced the bug and confirmed against `master` and this branch
to see the fix working
- [x] Ran full suite of Unreal tests
- [x] Manually tested Unreal Blackholio

Author: JasonAtClockwork

sdks/unreal/src/SpacetimeDbSdk/Source/SpacetimeDbSdk/Private/Connection/DbConnectionBase.cpp

@@ -1,7 +1,8 @@
 #include "Connection/DbConnectionBase.h"
-#include "Connection/DbConnectionBuilder.h"
+#include "Connection/DbConnectionBuilder.h"
 #include "Connection/Credentials.h"
 #include "Connection/LogCategory.h"
+#include "Containers/Ticker.h"
 #include "ModuleBindings/Types/ClientMessageType.g.h"
 #include "ModuleBindings/Types/SubscriptionErrorType.g.h"
 #include "Misc/Compression.h"
@@ -65,13 +66,48 @@ static FString DecodeReducerErrorMessage(const TArray<uint8>& ErrorBytes)
 }
 }
 
-UDbConnectionBase::UDbConnectionBase(const FObjectInitializer& ObjectInitializer)
-	: Super(ObjectInitializer)
-{
-	NextRequestId = 1;
-	NextSubscriptionId = 1;
-	ProcedureCallbacks = CreateDefaultSubobject<UProcedureCallbacks>(TEXT("ProcedureCallbacks"));
-}
+UDbConnectionBase::UDbConnectionBase(const FObjectInitializer& ObjectInitializer)
+	: Super(ObjectInitializer)
+{
+	NextRequestId = 1;
+	NextSubscriptionId = 1;
+	ProcedureCallbacks = CreateDefaultSubobject<UProcedureCallbacks>(TEXT("ProcedureCallbacks"));
+}
+
+void UDbConnectionBase::SetAutoTicking(bool bAutoTick)
+{
+	if (bIsAutoTicking == bAutoTick)
+	{
+		return;
+	}
+
+	bIsAutoTicking = bAutoTick;
+
+	if (bIsAutoTicking)
+	{
+		if (!TickerHandle.IsValid())
+		{
+			TickerHandle = FTSTicker::GetCoreTicker().AddTicker(FTickerDelegate::CreateUObject(this, &UDbConnectionBase::OnTickerTick));
+		}
+	}
+	else if (TickerHandle.IsValid())
+	{
+		FTSTicker::GetCoreTicker().RemoveTicker(TickerHandle);
+		TickerHandle.Reset();
+	}
+}
+
+void UDbConnectionBase::BeginDestroy()
+{
+	if (TickerHandle.IsValid())
+	{
+		FTSTicker::GetCoreTicker().RemoveTicker(TickerHandle);
+		TickerHandle.Reset();
+	}
+	bIsAutoTicking = false;
+
+	Super::BeginDestroy();
+}
 
 void UDbConnectionBase::Disconnect()
 {
@@ -216,8 +252,8 @@ void UDbConnectionBase::HandleWSBinaryMessage(const TArray<uint8>& Message)
 	});
 }
 
-void UDbConnectionBase::FrameTick()
-{
+void UDbConnectionBase::FrameTick()
+{
 	TArray<FServerMessageType> Local;
 	{
 		FScopeLock Lock(&PendingMessagesMutex);
@@ -236,31 +272,19 @@ void UDbConnectionBase::FrameTick()
 	{
 		//process the message, this will call DbUpdate or trigger subscription events as needed
 		ProcessServerMessage(Msg);
-	}
-}
-void UDbConnectionBase::Tick(float DeltaTime)
-{
-	if (bIsAutoTicking)
-	{
-		FrameTick();
-	}
-}
-
-TStatId UDbConnectionBase::GetStatId() const
-{
-	// This is used by the engine to track tickables, we return a unique stat ID for this class
-	RETURN_QUICK_DECLARE_CYCLE_STAT(UMyTickableObject, STATGROUP_Tickables);
-}
-
-bool UDbConnectionBase::IsTickable() const
-{
-	return bIsAutoTicking; 
-}
-
-bool UDbConnectionBase::IsTickableInEditor() const
-{
-	return bIsAutoTicking;
-}
+	}
+}
+
+bool UDbConnectionBase::OnTickerTick(float DeltaTime)
+{
+	if (HasAnyFlags(RF_BeginDestroyed | RF_FinishDestroyed) || !bIsAutoTicking)
+	{
+		return false;
+	}
+
+	FrameTick();
+	return true;
+}
 
 
 void UDbConnectionBase::ProcessServerMessage(const FServerMessageType& Message)

sdks/unreal/src/SpacetimeDbSdk/Source/SpacetimeDbSdk/Public/Connection/DbConnectionBase.h

@@ -1,7 +1,8 @@
 #pragma once
 
-#include "CoreMinimal.h"
-#include "UObject/NoExportTypes.h"
+#include "CoreMinimal.h"
+#include "Containers/Ticker.h"
+#include "UObject/NoExportTypes.h"
 #include "Types/Builtins.h"
 #include "Websocket.h"
 #include "Subscription.h"
@@ -114,8 +115,8 @@ struct THasOnUpdateDelegate<T, std::void_t<decltype(&T::OnUpdate)>> : std::true_
 {
 };
 
-UCLASS()
-class SPACETIMEDBSDK_API UDbConnectionBase : public UObject, public FTickableGameObject
+UCLASS()
+class SPACETIMEDBSDK_API UDbConnectionBase : public UObject
 {
 	GENERATED_BODY()
 
@@ -135,8 +136,8 @@ class SPACETIMEDBSDK_API UDbConnectionBase : public UObject, public FTickableGam
 	UFUNCTION(BlueprintCallable, Category="SpacetimeDB")
 	void FrameTick();
 
-	UFUNCTION(BlueprintCallable, Category="SpacetimeDB")
-	void SetAutoTicking(bool bAutoTick) { bIsAutoTicking = bAutoTick; }
+	UFUNCTION(BlueprintCallable, Category="SpacetimeDB")
+	void SetAutoTicking(bool bAutoTick);
 
 	/** Send a raw JSON message to the server. */
 	bool SendRawMessage(const FString& Message);
@@ -257,9 +258,11 @@ class SPACETIMEDBSDK_API UDbConnectionBase : public UObject, public FTickableGam
 	}
 
 
-protected:
+protected:
 
-	friend class UDbConnectionBuilderBase;
+	virtual void BeginDestroy() override;
+
+	friend class UDbConnectionBuilderBase;
 	friend class UDbConnectionBuilder;
 	friend class USubscriptionHandleBase;
 	friend class USubscriptionBuilder;
@@ -276,13 +279,7 @@ class SPACETIMEDBSDK_API UDbConnectionBase : public UObject, public FTickableGam
 	UFUNCTION()
 	void HandleWSBinaryMessage(const TArray<uint8>& Message);
 
-	virtual void Tick(float DeltaTime) override;
-
-	virtual TStatId GetStatId() const override;
-
-	virtual bool IsTickable() const override;
-
-	virtual bool IsTickableInEditor() const override;
+	bool OnTickerTick(float DeltaTime);
 
 	/** Internal handler that processes a single server message. */
 	void ProcessServerMessage(const FServerMessageType& Message);
@@ -407,6 +404,7 @@ class SPACETIMEDBSDK_API UDbConnectionBase : public UObject, public FTickableGam
 
 	UPROPERTY()
 	bool bIsAutoTicking = false;
+	FTSTicker::FDelegateHandle TickerHandle;
 	/** Guard to avoid repeatedly handling the same fatal protocol error. */
 	FThreadSafeBool bProtocolViolationHandled = false;