fix(wayland): open windows on compositors without xdg-decoration, viewporter or fractional scale

Window
- The constructor made a fractional scale, a toplevel decoration and a
  viewport from Device::fractionalScaleManager, Device::manager and
  Device::wpViewporter without looking at them. Device::handle_global
  binds those globals only when the compositor advertises them, and
  Initialize requires only wl_shm, wl_compositor and xdg_wm_base, so on a
  compositor without one of the three (GNOME's Mutter has no
  xdg-decoration) the constructor handed libwayland a null proxy and
  crashed before the window existed (#162). Each object is now made only
  when its global is there, which Resize and the destructor already
  assumed.
- The fractional scale needs the viewporter too: the preferred scale is
  applied through the viewport, which shows the buffer's physical pixels at
  width/scale x height/scale. A surface without a viewport is as large as
  its buffer, so there the scale stays 1, which keeps pointer and touch
  positions, configure sizes and the text-input caret, all converted by
  it, in physical pixels; the compositor scales the window up on a HiDPI
  output. A scale that changes after the constructor is still applied only
  by the next resize, which is #165.
- Without xdg-decoration the window has no title bar, since the library
  draws no client-side decorations.

Device
- The optional globals say they are optional, and that a request on a
  null proxy crashes.

Tests
- WindowOptionalGlobals: hides xdg-decoration, wp_viewporter and
  wp_fractional_scale_v1 from the Window one at a time and all at once,
  by nulling the Device statics after Initialize, and renders, resizes
  and closes a window each time without a protocol error. Before the fix
  it crashed on the window without xdg-decoration. A global the compositor
  does not offer is reported as a SKIP line, since the path that uses it
  goes untested there.

README
- Which Wayland protocols the window needs, and what it does without the
  optional ones.

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

README.md

@@ -85,7 +85,13 @@ shaded through an intersection shader with an any-hit cut-out.
   framing, input events. Pick a backend at build time via the target
   triple. The DOM backend routes every dynamic symbol through
   [additional/dom-env.js](additional/dom-env.js) and
-  [additional/dom-webgpu.js](additional/dom-webgpu.js).
+  [additional/dom-webgpu.js](additional/dom-webgpu.js). On Wayland the
+  window needs `wl_compositor`, `wl_shm` and `xdg_wm_base`, and uses
+  `xdg-decoration`, `wp_viewporter` and `wp_fractional_scale_v1` where the
+  compositor has them. Without xdg-decoration (GNOME) the window has no
+  title bar, as the library draws no client-side decorations; when either
+  of the other two is missing it draws at scale 1, and the compositor
+  scales it up on a HiDPI output.
 - **Device** *(Vulkan only)* — single-instance bring-up targeting
   `VK_EXT_descriptor_heap`; pipelines are created with
   `VK_PIPELINE_CREATE_2_DESCRIPTOR_HEAP_BIT_EXT` so there are no