feat: add typescript support for structs

- Allow [GenerateTypeScript] on struct declarations (managed and unmanaged)
- Managed structs use object-header wire format with non-nullable TS signatures;
  deserializeCore throws on null header instead of returning null
- Unmanaged structs use raw memory blit: field offsets and padding are computed
  at generation time and emitted as writeZeros/skipBytes calls
- Struct members in other types generate non-nullable TypeScript types
- Add MEMPACK043 diagnostic for Nullable<struct> members (use struct directly)
- Add writeZeros/skipBytes helpers to MemoryPackWriter/MemoryPackReader TS runtime
- Add BoundingBox (struct-in-struct) and GameObject (class + mixed structs) to sandbox
- Add comprehensive testStructs covering all struct combinations end-to-end

Author: dexsper

README.md

@@ -1211,10 +1211,13 @@ There are a few restrictions on the types that can be generated. Among the primi
 | `: ICollection<T>` | `T[] \| null` | Supports all `ICollection<T>` implemented type like `List<T>`
 | `: ISet<T>` | `Set<T> \| null` | Supports all `ISet<T>` implemented type like `HashSet<T>`
 | `: IDictionary<K,V>` | `Map<K, V> \| null` | Supports all `IDictionary<K,V>` implemented type like `Dictionary<K,V>`.
-| `[MemoryPackable]` | `class` | Supports class only
+| `[MemoryPackable]` | `class` | Supports class and struct (see notes below)
 | `[MemoryPackUnion]` | `abstract class` |
 
-`[GenerateTypeScript]` can only be applied to classes and is currently not supported by struct.
+`[GenerateTypeScript]` supports both classes and structs. There are two serialization modes depending on the struct type:
+
+- **Managed struct** (contains reference-type fields, e.g. `struct Foo { string Name; int Value; }`): uses the same object-header wire format as classes. The generated TypeScript `class` has non-nullable serialize signatures and omits the null-object-header write, matching the C# value-type semantics.
+- **Unmanaged struct** (contains only unmanaged fields, e.g. `struct Point { int X; int Y; }`): serialized as a raw memory blit with no object header, matching `WriteUnmanaged`/`ReadUnmanaged` in C#. The generated TypeScript `class` writes each field individually at its correct byte offset (including any padding required by natural alignment), and deserialize always returns a non-nullable value.
 
 ### Configure import file extension and member name casing
 

sandbox/SandboxWebApp/Controllers/MemoryPackController.cs

@@ -1,4 +1,4 @@
-using MemoryPack;
+using MemoryPack;
 using Microsoft.AspNetCore.Mvc;
 
 namespace SandboxWebApp.Controllers;
@@ -26,4 +26,16 @@ public NullableFloatTest PostNullableTest([FromBody] NullableFloatTest input)
 
         return ret;
     }
+
+    [Route("vector3")]
+    [HttpPost]
+    public Vector3 PostVector3([FromBody] Vector3 value) => value;
+
+    [Route("colorTag")]
+    [HttpPost]
+    public ColorTag PostColorTag([FromBody] ColorTag value) => value;
+
+    [Route("gameObject")]
+    [HttpPost]
+    public GameObject PostGameObject([FromBody] GameObject value) => value;
 }

sandbox/SandboxWebApp/Models.cs

@@ -1,4 +1,4 @@
-using MemoryPack;
+using MemoryPack;
 using System.ComponentModel;
 using System.Security.Principal;
 
@@ -205,3 +205,38 @@ public partial class NullableFloatTest
     public float? NullableFloat { get; set; }
     public double? NullableDouble { get; set; }
 }
+
+[MemoryPackable]
+[GenerateTypeScript]
+public partial struct Vector3
+{
+    public float X { get; set; }
+    public float Y { get; set; }
+    public float Z { get; set; }
+}
+
+[MemoryPackable]
+[GenerateTypeScript]
+public partial struct ColorTag
+{
+    public string? Name { get; set; }
+    public int Code { get; set; }
+}
+
+[MemoryPackable]
+[GenerateTypeScript]
+public partial struct BoundingBox
+{
+    public Vector3 Min { get; set; }
+    public Vector3 Max { get; set; }
+}
+
+[MemoryPackable]
+[GenerateTypeScript]
+public partial class GameObject
+{
+    public string? Name { get; set; }
+    public Vector3 Position { get; set; }
+    public BoundingBox Bounds { get; set; }
+    public ColorTag Tag { get; set; }
+}

sandbox/SandboxWebApp/Pages/Index.cshtml

@@ -1,4 +1,4 @@
-@page
+@page
 @model IndexModel
 @{
     ViewData["Title"] = "Home page";
@@ -11,6 +11,9 @@
     import { testNullableFloatWithNulls } from "./js/file.js";
     import { hoge } from "./js/file.js";
     import { huga } from "./js/file.js";
+    import { testVector3 } from "./js/file.js";
+    import { testColorTag } from "./js/file.js";
+    import { testStructs } from "./js/file.js";
 
     //hoge();
     //huga();
@@ -20,6 +23,10 @@
     testNullableFloatWithValues();
     testNullableFloatWithNulls();
 
+    testVector3();
+    testColorTag();
+    testStructs();
+
 </script>
 
 <div class="text-center">