Fix Metal device edge cases; keep reporting the host GPU

From #61, without the default "AMD Radeon Pro 5500M" / 4 GB identity: the
host GPU's name and Vulkan working set stay the default for every app, and
the existing DARLING_METAL_GPU_NAME and DARLING_METAL_VRAM_MB overrides
remain the opt-in. Reporting 4 GB on a 2 GB card invites allocation
failures, and under-reports larger cards.

Kept from #61:
- registryID returns MTLDeviceInfo::kDefaultRegistryID instead of 0; a
  real Mac never reports 0 and apps key devices by it.
- Vertex buffer layout and attribute arrays release the old item after
  retiring it; the retire step read the item after the release could free it.
- newDepthStencilState, newSamplerState and the device name return nil (or
  the fallback name) when Indium throws, instead of unwinding through
  Objective-C.
- MTLDepthStencilGetIndium is declared only with DARLING_METAL_ENABLED.
- The replaceRegion trace probes at most `width` bytes, which stays inside
  the first row for every pixel format.

metal.patch is regenerated in its existing file order, so the diff is
these changes only. tests/test_metal_device_info.py compiles the host
check against MTLDeviceInfo.h as shipped in the patch and runs in CI.

Split from #61.

Co-authored-by: DevWebeloper <[email protected]>
Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/TESTING.md

@@ -23,7 +23,7 @@ c++ -std=c++17 -I build/darling-src/src/external/metal/private-include \
 build/test-metal-device-info
 ```
 
-Expected: `METAL_DEVICE_INFO failures=0 pass=1`. It covers how `MTLDevice.name` turns Vulkan names into macOS style (`AMD Radeon RX 6800 XT (RADV NAVI21)` becomes `AMD Radeon RX 6800 XT`, `Intel(R) UHD Graphics 630 (CML GT2)` becomes `Intel UHD Graphics 630`, NVIDIA names stay as they are), the `DARLING_METAL_VRAM_MB` parser, and the working-set sum over Vulkan heaps.
+Expected: `METAL_DEVICE_INFO failures=0 pass=1`. It covers how `MTLDevice.name` turns Vulkan names into macOS style (`AMD Radeon RX 6800 XT (RADV NAVI21)` becomes `AMD Radeon RX 6800 XT`, `Intel(R) UHD Graphics 630 (CML GT2)` becomes `Intel UHD Graphics 630`, NVIDIA names stay as they are), the `DARLING_METAL_VRAM_MB` parser, the working-set sum over Vulkan heaps, and a non-zero `registryID`. `python3 -m unittest tests.test_metal_device_info` runs the same check against the header in `patches/metal.patch`, so it also works without a prepared source tree; CI runs it.
 
 The LLVM version check compiles Iridium's actual dynamic loader against small stub libraries. It verifies that a matching major initializes, older/newer majors produce a version mismatch, and a missing library fails initialization. It does not start Darling. The native AIR translator (`python3 tools/build-riot-air-check.py --native`) selects both headers and the shared library from the same `llvm-config`; its build prints those paths so shader results can be attributed to the tested LLVM installation.