this was initially part of draw-preview but was later moved to a
separate property because it was deemed useful outside of just
thumbnail preview. however this causes bugs when a thumbnailer
observes draw-request and the draw rectangle doesn't change (e.g
due to getting clamped around the border).
add back hover-sec which makes the draw-request more self
contained and removes this footgun.
Fixes: https://github.com/mpv-player/mpv/pull/17518#discussion_r3256017469
NRK
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