gui: reclaim layout callback lifetimes

[GGRei]

Summary

This uses the closure lifetime/reclaim API to reclaim transient layout callbacks in v-gui.

Window.update() now builds each layout tree inside a layout callback lifetime frame, keeps the current layout alive, and reclaims old frame-owned closure contexts after the new layout has been installed.

Persistent callbacks created during layout, such as animations, hover-created callbacks, async data sources, CRUD saves, and deferred drag/drop callbacks, are kept alive outside the transient reclaim scope when needed.v

Codex review validation is available here: GGRei#2

Fix #58

Changes

• Add a small v-gui wrapper around the V closure lifetime API.
• Track layout callback closures during Window.update().
• Reclaim old layout-owned callbacks after replacing the layout tree.
• Dispose layout callback lifetime state during window cleanup.
• Keep persistent animations and hover-created callbacks outside frame reclaim.
• Pin async data-grid and listbox source callbacks until completion/abort.
• Pin async data-grid CRUD save callbacks until queued completion is applied.
• Snapshot drag-reorder layout transitions before user drop handlers can rebuild layout.
• Add regression coverage for layout callback memory growth, current-layout callback survival, persistent callbacks, async source callbacks, CRUD callbacks, drag reorder ordering, mouse lock callbacks, and idempotent cleanup.

Dependency

This PR depends on vlang/v#27483.

⚠️ Until vlang master includes vlang/v#27483, CI failures are expected because this PR uses the new closure lifetime/reclaim API. Please rerun the checks once the compiler PR is merged.

Tests

/home/alex-portable/external_work/vlang_closure_lifetime_api_20260617/./v -o v_gui_verify cmd/v

/home/alex-portable/external_work/vlang_closure_lifetime_api_20260617/v_gui_verify test _window_lifetime_test.v
/home/alex-portable/external_work/vlang_closure_lifetime_api_20260617/v_gui_verify test _drag_reorder_test.v

git diff --check