fix(render3d): nothing allocated in the steady state - the Vulkan allocator reuses its records

gvk_mem_new made a one-slot []pointer per allocation, and turned the requirement's size and
alignment into strings to read them as ints; gvk_list_drop_last rebuilt the spare-record list to
drop its last entry; gvk_mem_id did the string round trip on every free. One slot is kept
(gvk_map_slot), int() truncates a long, the spare list pops. Every Text.to_int(string(x)) in
render3d is int(x) now.

Vk.heap_bytes() (vk_mac.ll: malloc_zone_statistics' size_in_use; 0 on Windows) and
examples/rendering/steady.ludic, in the suite: a buffer released and made again 5000 times and
600 whole frames gain 0 bytes each - the allocator before this, 1,120,000 over the 5000.

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

packages/ludic.render3d/env.ludic

@@ -201,6 +201,7 @@ export state Render3dState {
   gvk_inflight: int = -1
   gvk_nopool: bool = false
   gvk_bc_said: int = 0              # attachments refused for being compressed, said so far
+  gvk_map_slot: []pointer = null    # gvk_mem_new's mapped-pointer slot, made once
   gvk_has_bc: bool = false          # textureCompressionBC: .dds textures are uploaded compressed
   # R3D_VK_PROF: Vulkan objects made and destroyed, reported every 120 frames
   gvk_mk_img: int = 0