fix: preserve fullscreen state when moving window between workspaces

[mayakwd]

Following up #2099.
Fixes the issue where moving a full-screen window (e.g., Chrome with a full-screen video) between workspaces causes the client to exit full-screen.

Root cause: move_window calls unmap_surface, which internally calls remove_fullscreen(). This sends an intermediate configure with set_fullscreen(false) before map_fullscreen(), and then map_fullscreen () re-applies it on the destination workspace.
Chrome sees the intermediate "not a full-screen" configure and cancels video full-screen.

Fix explanation:

• Added Workspace::take_fullscreen() — a silent counterpart to remove_fullscreen() that extracts the fullscreen state without notifying the client (no set_fullscreen(false), no send_configure(), no exit animation).
• In move_window, fullscreen windows are detected and handled via take_fullscreen() instead of unmap_surface(). The destination workspace's map_fullscreen() then sends a single configure with fullscreen state preserved.
• remove_fullscreen() and unmap_surface() remain unchanged — all other code paths (close, minimize, unfullscreen, drag-move) still go through the original flow with proper client notification and exit animation.

What I tested:

• Chrome with fullscreen video > Move to another workspace > Video stays full-screen
• Firefox with fullscreen video > Move to another workspace > Video stays full-screen (regression test)
• Fullscreen game (Death Stranding) and Steam in Big-Picture mode successfully moved through workspaces without losing full-screen state

What I didn't test:

• Moving windows through workspaces attached to different displays (I don't have such hw setup), but it still should work, since toplevel_leave_output and toplevel_enter_output handle this case.

UPD
Added agreement section from PR template:

• I have disclosed use of any AI generated code in my commit messages.
• I understand these changes in full and will be able to respond to review comments.
• My change is accurately described in the commit message.
• My contribution is tested and working as described.
• I have read the Developer Certificate of Origin and certify my contribution under its conditions.

[Drakulix]

Thanks. This looks good apart from some nitpicks.

[Drakulix]

Suggested change

	let surface = self.fullscreen.take()?;
	let surface = self.fullscreen.take_if(|s| s.ended_at.is_none())?;

Would be a bit cleaner here and avoid the whole condition.

[mayakwd]

Good point! Done.

[Drakulix]

Could this for symmetry with remove_fullscreen please also return the surface. That is easy enough to skip over in move_window.

[mayakwd]

Done