Added a basic MemoryArena.

Added one scratch, one engine and one game arena.
Converted the game alloc to arena + the display stuff.
WIP

Made using Antigravity+gemini

AgentData/MemoryArena.md

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+# Memory System Status & Migration Plan
+
+## Completed Work
+
+### Core Systems
+- **MemoryArena**: Implemented linear allocator with alignment, markers, and reset support.
+- **Global Arenas**:
+  - `ScratchArena` (64MB): Transient per-frame memory.
+  - `EngineArena` (256MB): Persistent engine memory (internal).
+  - `GameArena` (512MB): Persistent game memory (exported to Game DLL).
+- **Helpers**: Added `ArenaPushType<T>` and `ArenaPushArray<T>` with automatic zero-initialization.
+
+### Migrated Subsystems
+- **Display**: `Win32Window` and `Win32DisplayDevice` now use `EngineArena`.
+- **Game Entities**: `Entity.h` uses `GameArena` for entity allocation; manual `free` calls removed from `game.cpp`.
+
+## Remaining Work
+
+The following subsystems still use legacy `malloc`/`calloc`/`realloc`/`free` and need to be migrated.
+
+### Hot Reload System
+- **Files**: `Core/HotReload/HotReload.cpp`, `Core/HotReload/Win32/Win32HotReload.cpp`
+- **Allocations**: `DLLFullPath`, `LockFullPath`, `tempDllPath`.
+- **Strategy**: 
+  - Use `EngineArena` for persistent paths (`DLLFullPath`, `LockFullPath`).
+  - Use `ScratchArena` for temporary paths (`tempDllPath`).
+
+### IO System
+- **Files**: `Core/HAL/IO/IOStream.cpp`, `Core/HAL/IO/Win32/Win32IOStream.cpp`
+- **Allocations**: `IOStream` instance, data buffers, `Win32IOStreamDataPayload`.
+- **Challenge**: `Realloc` is used for growing buffers.
+- **Strategy**: 
+  - `IOStream` struct -> `ScratchArena` (if transient) or `EngineArena`.
+  - Buffers: Evaluate if `ArenaPush` with large enough capacity is sufficient, or implement a growable buffer on top of arena (or use `std::vector` with custom allocator if absolutely needed, but prefer simple fixed max size if possible).
+
+### Graphics / Debug
+- **Files**: `Graphics/DebugDisplayRenderer.cpp`
+- **Allocations**: `DepthTestedVertices`, `OverlayVertices`.
+- **Strategy**: Use `EngineArena` or a dedicated `RenderArena` if these are persistent. If per-frame, move to `ScratchArena`.
+
+### Shader Compiler
+- **Files**: `JulietShaderCompiler/ShaderCompiler.cpp`
+- **Allocations**: Argument arrays, file buffers.
+- **Strategy**: Use `ScratchArena` for all compilation tasks as they are transient.
+
+### Filesystem
+- **Files**: `Core/HAL/Filesystem/Filesystem.cpp`
+- **Allocations**: `CachedBasePath`.
+- **Strategy**: Migrate to `EngineArena` (persistent).