vulkan: use sync objects if possible

[mahkoh]

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[Copilot]

Pull request overview

This PR updates the Vulkan explicit-sync path to prefer DRM syncobj-backed timeline semaphores when supported, falling back to fences/sync files otherwise, and threads a shared eventfd cache through the rendering/copy stack to efficiently wait on syncobj points.

Changes:

• Add a vulkan_core sync layer (VulkanTimelineSemaphore, VulkanSync) that can export either a fence-based sync file or a syncobj point.
• Introduce gfx_api::FdSync to unify “sync file vs syncobj point” handling across Vulkan/GL/Metal/backends and buffer reservation plumbing.
• Add EventfdCache and pass it through compositor/portal/screenshot/copy-device paths to support syncobj-point waiting via eventfds.

Reviewed changes

Copilot reviewed 37 out of 37 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/vulkan_core/timeline_semaphore.rs	Creates/export-checks a timeline semaphore and maps it to a DRM syncobj.
src/vulkan_core/sync.rs	Adds VulkanSync abstraction (fence vs timeline semaphore) and sync creation for queue submissions.
src/vulkan_core/fence.rs	Refactors fence into generic VulkanFence<D> using VulkanDeviceInf.
src/vulkan_core/device.rs	Introduces VulkanDeviceInf trait to unify device access for core sync primitives.
src/vulkan_core.rs	Adds core error variants and feature probing for timeline semaphore export support.
src/video/drm/sys.rs	Adds timeline handle-to-fd flag, query ioctl wrapper, and extends handle-to-fd API with point.
src/video/drm/syncobj.rs	Adds syncobj id, query-last-signaled, and blocking export path for sync files from syncobj points.
src/video/drm.rs	Re-exports get_drm_nodes_from_dev and extends DrmError for syncobj query/export.
src/utils/stack.rs	Adds Stack::len() (used by eventfd cache tests).
src/state.rs	Wires EventfdCache through state and changes render sync type to FdSync.
src/portal/ptl_display.rs	Passes EventfdCache into gfx context creation.
src/portal.rs	Adds EventfdCache to portal state initialization.
src/main.rs	Adds new eventfd_cache module.
src/it/test_client.rs	Updates screenshot path to supply EventfdCache to buffer readback.
src/ifs/wl_surface.rs	Switches buffer reservation sync tracking to FdSync and sync-file extraction when needed.
src/ifs/ext_image_copy/ext_image_copy_capture_frame_v1.rs	Updates capture-frame callback signatures to return FdSync.
src/gfx_apis/vulkan/transfer.rs	Uses VulkanDeviceSyncExt to signal either syncobj or fence and waits via FdSync.
src/gfx_apis/vulkan/shm_image.rs	Updates async upload/download sync plumbing to use VulkanSync/FdSync.
src/gfx_apis/vulkan/renderer.rs	Introduces per-render/transfer timeline semaphores and switches release signaling to VulkanSync/FdSync.
src/gfx_apis/vulkan/image.rs	Updates framebuffer render return type to FdSync.
src/gfx_apis/vulkan/device.rs	Implements VulkanDeviceInf, wires EventfdCache, and computes timeline-export support.
src/gfx_apis/vulkan.rs	Threads EventfdCache into Vulkan context/allocator creation and defines core sync aliases.
src/gfx_apis/gl/renderer/framebuffer.rs	Updates GL rendering to return FdSync.
src/gfx_apis/gl.rs	Wraps produced sync files into FdSync and uses AcquireSync::get_sync_file() for imports.
src/gfx_apis.rs	Threads EventfdCache into gfx context creation dispatch.
src/gfx_api.rs	Introduces FdSync, ReservedSyncobjPoint, updates AcquireSync and BufferResv API.
src/eventfd_cache/tests.rs	Adds tests for eventfd cache recycling behavior.
src/eventfd_cache.rs	Adds EventfdCache and Eventfd for async waits and recycling.
src/cursor_user.rs	Updates cursor swap-buffer sync type to FdSync.
src/copy_device.rs	Updates copy device to use VulkanSync/timeline semaphore when possible and adopt FdSync.
src/compositor.rs	Initializes and stores EventfdCache, passes it to gfx/copy device setup.
src/cli/screenshot.rs	Creates an EventfdCache for screenshot allocator path and passes it into Vulkan allocator creation.
src/backends/metal/video.rs	Updates cursor sync tracking to FdSync.
src/backends/metal/transaction.rs	Replaces per-syncfile poll loop with FdSync::signaled_blocking.
src/backends/metal/present.rs	Uses FdSync for cursor and framebuffer wait paths.
src/backends/metal/allocator.rs	Updates render/copy sync plumbing to FdSync and uses AcquireSync::from_fd_sync.
src/backend.rs	Updates HardwareCursorUpdate::swap_buffer to take FdSync.

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