Fix unsound Send impl for inspector::CharacterArray (T: Copy -> T: Sync)

[fairfairfair-210]

Fix unsound Send impl for inspector::CharacterArray (T: Copy → T: Sync)

CharacterArray<'a, T> is semantically a borrowed slice &[T] (safe From<&[T]> constructor, Deref<Target = [T]>), but its handwritten Send impl requires T: Copy while the Sync impl on the same type correctly requires T: Sync.

For a &[T]-like type the correct condition is T: Sync in both directions (&[T]: Send ⇔ T: Sync). T: Copy neither implies nor is implied by T: Sync — e.g. &'static Cell<i32> is Copy but !Sync, so safe code can currently send CharacterArray<'static, &'static Cell<i32>> across threads and obtain shared &Cell<i32> accesses — a data race without any unsafe at the use site.

The fix tightens the Send bound to T: Sync. All in-tree instantiations are u8/u16 (both Sync), so nothing else is affected.

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