implement :cursor zoommode for Axis3 with :free viewmode

[bjarthur]

per the title, this PR implements Axis3(zoommode = :cursor, viewmode = :free).

gemini wrote it. tried claude and it's response didn't work. please review carefully.

[bjarthur]

with this PR:

makie-zoomcursor.mov

julia> using GLMakie
julia> f = Figure()
julia> a = Axis3(f[1,1], zoommode = :cursor, viewmode = :free)
julia> s = scatter!(a, rand(Point3f, 10))

not sure how to make a test for a video.