Use `GHC2024` in `singletons-th` and `singletons-base`

[RyanGlScott]

GHC 9.10 introduces the GHC2024 language extension set. As compared to GHC2021, this enables several additional language extensions by default, and several of these are ones that are commonly sprinkled throughout the code (e.g., DataKinds). Following in the footsteps of https://github.com/goldfirere/singletons/issues/508, we should make GHC2024 the default-language in the .cabal files for singletons-th and singletons-base.