[marcoallegretti]

Fixes #153.

Presentation hints currently become visible as soon as set_presentation_hint is dispatched. Destroying the control also resets the hint immediately. Both changes are double-buffered by the Wayland protocol, so a repaint before the next surface commit can observe the wrong hint.

Store presentation hints in Smithay's cached surface state and read only the current value. Keep control-object existence immediate for duplicate-object detection. This also follows synchronized subsurface transactions without changing TTY tearing eligibility, configuration overrides, or hardware checks.

API impact: no public Rust or TypeScript API changes. Hint changes become observable at the protocol-defined commit boundary.

Validation:

• Before the fix, three socket-pair Wayland regression tests failed for an uncommitted async hint, an early destroy reset, and an early synchronized-subsurface update.
• cargo test -p shojiwm_lib --lib --locked protocols::tearing_control::tests: 4 passed, none ignored. Covers async/vsync commit boundaries, last pending hint, persistence across commits, destroy/reset, recreation before commit, and synchronized subsurfaces.
• cargo test -p shojiwm_lib --lib --locked: 317 passed, 1 failed, 4 ignored. The failure is xwayland_satellite::tests::skips_a_display_with_an_occupied_abstract_socket, which cannot prepare its socket directory because /tmp/.X11-unix is not writable. That code is unchanged.
• Formatting checks for both changed Rust files and git diff --check pass.