feat(render3d): 23.4 - model_release, shared textures counted, and scatter layers sized to what they hold

- model_release(model) frees each primitive's mesh, and each texture once no other model uses it:
  the glTF texture cache counts the primitives using each texture (a path loaded again, and a LOD
  chain borrowing its LOD0's material, each take a reference); the last one frees the texture and
  forgets it along with any remembered material naming it, so a later load is a fresh one
- a scatter layer's instance and sort arrays start at 256 and double as layer_add or a stream
  fills them, to the layer's cap, instead of the whole cap up front (0.4 GB in Maroon Lake)
- gvk_tex_read's copy struct comes from the scratch ring
- examples/rendering/release.ludic holds it (RELEASE OK on Vulkan and OpenGL), in the suite

smooth renders pixel-identical before and after (max |d| 0). ludic-dev test 306/306.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.render3d/gpu_vk_res.ludic

@@ -409,7 +409,7 @@ function gvk_tex_read(render3d_st: mut Render3dState, tex: int, ifmt: int, w: in
   let depth = gvk_is_depth(ifmt)
   let cb = gvk_once_begin(render3d_st)
   gvk_barrier(render3d_st, cb, image, depth, 0, 1, 1, VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL, VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL)
-  let bic = bytes(VkBufferImageCopy_sizeof)
+  let bic = gvk_tmp(render3d_st, VkBufferImageCopy_sizeof)
   Vk.zero(bic, VkBufferImageCopy_sizeof)
   if depth { Vk.put_i32(bic, VkBufferImageCopy_imageSubresource + VkImageSubresourceLayers_aspectMask, VK_IMAGE_ASPECT_DEPTH_BIT) }
   else { Vk.put_i32(bic, VkBufferImageCopy_imageSubresource + VkImageSubresourceLayers_aspectMask, VK_IMAGE_ASPECT_COLOR_BIT) }