configurable: add Configurable

[mahkoh]

No description provided.

[Copilot]

Pull request overview

This PR adds a generic configurable scheduling path to coalesce and flush configure events across several surface-like objects in the compositor.

Changes:

• Introduces Configurable, ConfigureGroups, and async commit/apply handlers.
• Migrates xdg surfaces, layer surfaces, tray items, and session lock surfaces to scheduled configure delivery.
• Adds a reusable Size type and async stack helper utilities.

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/configurable.rs	Adds grouped configure scheduling and flushing infrastructure.
src/compositor.rs	Registers configurable commit/apply handlers and initializes configure groups.
src/state.rs	Stores configure groups and exposes schedule_configure.
src/utils/stack.rs	Adds swap support and AsyncStack.
src/rect.rs	Re-exports Size and adds Rect::size2.
src/rect/size.rs	Adds non-negative size wrapper.
src/main.rs	Registers the new module.
src/ifs/wl_surface/xdg_surface.rs	Converts xdg configure delivery to Configurable.
src/ifs/wl_surface/xdg_surface/xdg_toplevel.rs	Captures toplevel configure data for delayed flushing.
src/ifs/wl_surface/xdg_surface/xdg_popup.rs	Captures popup configure/reposition data for delayed flushing.
src/ifs/wl_surface/zwlr_layer_surface_v1.rs	Schedules layer-surface configures except for immediate-configure quirks.
src/ifs/wl_surface/tray.rs	Converts tray item configure flow to scheduled configures.
src/ifs/wl_surface/tray/jay_tray_item_v1.rs	Implements configurable flushing for tray items.
src/ifs/wl_surface/ext_session_lock_surface_v1.rs	Schedules lock-surface configures.
src/ifs/ext_session_lock_v1.rs	Initializes lock-surface configurable data.
src/tree/output.rs	Adjusts tray configure calls for Rc receiver.
src/ifs/zxdg_toplevel_decoration_v1.rs	Uses scheduled xdg configure after decoration mode changes.
src/ifs/zwlr_layer_shell_v1.rs	Removes obsolete dead-code expectation.
src/bugs.rs	Removes obsolete dead-code expectation.

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