Reminder: things to do if we switch to requiring Julia >= 1.10

[fingolfin]

• always use jl_reinit_foreign_type (introduced in Julia 1.9 IIRC) and drop a bunch of code from the C kernel, GAP_jll and GAP.jl itself
• add a package extension to GAP.jl which gets loaded when Nemo is also present, and move the code for conversion to/from Nemo types like ZZRingElem, QQMatrix etc. from Oscar.jl into that
• drop setglobal! alternate code
• check for VERSION checks that could be removed
• ...