handles: one interleaved vertices/indices arena

Geometry becomes a span in a single 80-byte interleaved `vertices` array
plus a span in a single `indices` array, allocated through the core's
span allocator instead of one arena array per mesh attribute. Draws are
always indexed with baseVertex; face-material overrides emit one draw per
run of same-material faces rather than one per face. Vertex data is
validated as a whole before any span is touched, same-geometry mutations
are serialised, and render signal 4 is held across a span change until
the graph reflecting it is published. Sibling arrays grow to the primary
array's capacity in one batch; reserve() takes vertex/index totals.

Amp-Thread-ID: https://ampcode.com/threads/T-01a0b2dd-db32-712d-99ce-12ce4a86d979
Co-authored-by: Heaust Azure <heaust.azure@gmail.com>

server/web/assets/yawn.d.ts

@@ -87,7 +87,12 @@ declare module "@yawn/handles" {
       stride: number,
       format: "f32" | "u32" | "i32",
     ): Promise<SharedRows>;
-    reserve(additional: { nodes?: number; materials?: number }): Promise<void>;
+    reserve(additional: {
+      nodes?: number;
+      materials?: number;
+      vertices?: number;
+      indices?: number;
+    }): Promise<void>;
     batchWrites<T>(operation: () => T): T;
     batchGraphUpdates<T>(operation: () => T | Promise<T>): Promise<T>;
     compileRenderGraph(serialized: string): Promise<string>;
@@ -149,18 +154,22 @@ declare module "@yawn/handles" {
   export interface MeshOptions extends NodeOptions {
     geometryId?: number;
     material?: PBRMaterial;
-    vertexData?: Partial<Record<VertexKind, ArrayLike<number>>>;
+    vertexData?: VertexStreams;
     visible?: boolean;
   }
+  export type VertexStreams = Partial<Record<VertexKind, ArrayLike<number>>>;
   export class Mesh extends Node {
     constructor(scene: Scene, options?: MeshOptions);
     geometryId: number;
-    vertexCount: number;
-    indexCount: number;
+    readonly vertexCount: number;
+    readonly indexCount: number;
     isVisible: boolean;
     material: PBRMaterial;
     clone(options?: Omit<MeshOptions, "geometryId" | "vertexData">): Mesh;
-    setVertexData(kind: VertexKind, data: ArrayLike<number>): Promise<this>;
+    setVertexData(
+      kind: VertexKind | VertexStreams,
+      data?: ArrayLike<number>,
+    ): Promise<this>;
     setMaterialForFaces(
       material: PBRMaterial,
       faces: number | number[],