If the camera track has already ended by the time the blur processor is
applied to it, MediaStreamTrackProcessor cannot be constructed and
setProcessor rejects. Both call sites used `void`, so this surfaced as
Unhandled promise rejection: TypeError: Failed to construct
'MediaStreamTrackProcessor': Input track cannot be ended
(element-call-rageshakes#17225). Skip ended tracks, and catch and log
processor attach/detach failures instead of leaking them.
* Replace useContext with use
The docs recommend the use hook because it is simpler and allows itself to be called conditionally.
* Simplify our context providers
React 19 lets you omit the '.Provider' bit.
Matthew Hodgson