Metal: texture readback, allocation failure reporting and batched clear rects

[navjack]

• Copy texture regions into CPU-visible buffers so texture readback works
  on the Metal backend, as it does on D3D12 and Vulkan.
• createTexture and createBuffer return nullptr when the Metal allocation
  fails instead of handing back an object wrapping a null resource, so
  callers can fall back.
• clearDepthStencil submits rect lists longer than the per-call limit in
  batches, as the D3D12 backend does, instead of asserting.

Notes

Extracted from the LostOdysseyRecomp macOS Metal port. Two project-specific pieces of the original change (a device-level shaderFormat capability and a RenderSwapChain::getFormat() override) are intentionally left out, so this applies to main on its own.

Testing

• Used during gameplay in the LostOdysseyRecomp macOS Metal port (Apple M4 Pro, macOS 27, Xcode 27), which reads back resolved textures and clears with long rect lists.
• -fsyntax-only compile of plume_metal.cpp on arm64 macOS against current main passes.

🤖 Generated with Claude Code

[DarioSamo]

AI-generated contributions are not accepted, especially ones with Claude as the co-author. No copyright will be given to Anthropic in any of my projects.