`merge_correlations!` should support `SampledCorrelationsStatic`

This issue was identified by Paul Neves on Slack. Maybe this implementation will work: ```jl function merge_correlations(scs::Vector{SampledCorrelationsStatic}) sc_merged = merge_correlations([sc.parent for sc in scs]) return Sunny.SampledCorrelationsStatic(sc_merged) end ```