fix(render3d): three leaks in Vulkan play - sampler keys, mip blits, a program per actor

- gvk_sampler built a key string on every call it was reached (a texture read two ways in turn
  misses its per-texture cache each time); samplers are found by their seven numbers instead
- gvk_tex_mips_into allocated a VkImageBlit per level, every frame (the exposure measure's
  chain); it comes from the scratch ring, as does gvk_tex_grow_mips's copy
- gvk_program_new made a new program - modules, pipelines - on every call, and every actor asks
  for one; a variant is now made once and shared (a program is immutable), and one that cannot
  be made stays 0 for every later asker

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

packages/ludic.render3d/env.ludic

@@ -354,7 +354,7 @@ export state Render3dState {
   gvk_unpack_swap: bool = false     # GL_UNPACK_SWAP_BYTES: 16-bit PNG samples arrive big-endian
   gvk_st_buf: long = 0
   gvk_st_mem: long = 0
-  gvk_smp_keys: []string = null
+  gvk_smp_keys: []int = null        # 7 numbers per sampler: filters, wraps, compare, anisotropy, bias
   gvk_smp: []long = null
   gvk_buf: []long = null
   gvk_buf_mem: []long = null