perf(render3d): Vulkan device memory in blocks, and a shadow map that survives running out of it

- A block sub-allocator: 64 MB blocks per memory type, images and buffers kept apart, first fit with
  alignment, freed ranges merged and empty blocks given back; anything over 16 MB still gets its own
  allocation. The self-tests' second world holds 94 allocations instead of 8735 (the driver's limit
  refused a shadow map before). Camp bench unchanged, 105.3 fps.
- shadow_set_res keeps the size that worked when the card has no memory for the new one, and records
  it in shadow_refused, instead of ending with no shadow map; gpu_tex_ok says whether a texture has an
  image behind it.
- Image barriers skip an image that was never made (a failed allocation used to crash there), and
  R3D_VK_ERRLOG=<file> appends every Vulkan failure line by line, so a crash no longer takes the
  message with it.
- R3D_VK_PROF reports draws asked for and not made, so a layer missing from a frame is never silent.

Validation on (VK_INSTANCE_LAYERS): the game's self-tests 61 OK, 0 errors, on the RTX 3070 Ti.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/ludic.render3d/shadow.ludic

@@ -6,6 +6,7 @@
 
 # the size of each cascade's depth layer; shadow_set_res changes it at run time
 var shadow_res: int = 2048
+var shadow_refused: int = 0          # the last size the graphics card had no memory for (0: none)
 const SHADOW_CASCADES: int = 5
 
 var sh_tex: int = 0
@@ -42,10 +43,27 @@ function shadow_init() -> void {
 # texel size from the map itself, so nothing else has to follow.
 function shadow_set_res(r: int) -> void {
   if r < 256 or r == shadow_res { return }
+  let was = shadow_res
   shadow_res = r
   if sh_tex == 0 { return }
   gpu_tex_free(sh_tex)
   shadow_make_tex()
+  # not enough video memory for that size: go back to the one that worked, and smaller again if even
+  # that is refused now, rather than ending with no shadow map at all
+  if not gpu_tex_ok(sh_tex) {
+    shadow_refused = r
+    print(`r3d: shadows: no memory for {r} x {r} cascades; keeping {was}`)
+    var size = was
+    shadow_res = size
+    gpu_tex_free(sh_tex)
+    shadow_make_tex()
+    while not gpu_tex_ok(sh_tex) and size > 512 {
+      size = size / 2
+      shadow_res = size
+      gpu_tex_free(sh_tex)
+      shadow_make_tex()
+    }
+  }
 }
 
 function shadow_make_tex() -> void {