DataInspector shall show Gray(val) for gray images

[MariusDrulea]

The tooltip shall be img[7, 4] = Gray(0.58)

using GLMakie
using ColorTypes

fig = Figure()
image(fig[1, 1], Gray.(rand(10, 10)), axis=(yreversed=true,), interpolate=false)
DataInspector(fig)
fig

[ffreyer]

This should only require a new overload for these functions: https://github.com/MakieOrg/Makie.jl/blob/182c3faaa958f06c5d3e5ea81356925d69881d1e/src/interaction/inspector.jl#L37-L46