feat(lowlevel): add VirtualStack, update allocators, docs

Introduce VirtualStack allocator, refactor memory management to use virtual memory stacks, and update documentation.

Added VirtualStack as a new stack allocator using virtual memory, replaced Stack with VirtualStack in allocation manager and related APIs, and updated TempJobAllocator to use VirtualArena. Introduced AllocationManagerInitOpts for allocator configuration. Replaced ENABLE_COLLECTION_CHECKS with ENABLE_SAFETY_CHECKS for safety checks. Removed Result.cs and updated project files and examples. Added comprehensive README files for all major packages and improved root documentation.

BREAKING CHANGE: Stack allocator replaced by VirtualStack; TempJobAllocator and AllocationManager initialization signatures changed; Result types removed.

Misaki.HighPerformance.LowLevel/Buffer/VirtualArena.cs

@@ -6,8 +6,17 @@ namespace Misaki.HighPerformance.LowLevel.Buffer;
 /// <summary>
 /// A thread-safe memory management structure that reserves a large virtual address space and commits physical memory on demand as allocations are made.
 /// </summary>
-public unsafe struct VirtualArena
+public unsafe struct VirtualArena : IMemoryAllocator<VirtualArena, VirtualArena.CreationOptions>
 {
+    public struct CreationOptions
+    {
+        public nuint reserveCapacity;
+    }
+    public static VirtualArena Create(in CreationOptions opts)
+    {
+        return new VirtualArena(opts.reserveCapacity);
+    }
+
     private const nuint _PAGE_SIZE = 64 * 1024;
 
     private byte* _baseAddress;
@@ -95,6 +104,11 @@ public unsafe struct VirtualArena
         return ptr;
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public readonly void Free(void* ptr)
+    {
+    }
+
     /// <summary>
     /// Resets the arena.
     /// </summary>