Switch to effects system from `@pure` on 1.9?

Since `@pure` is a no-op after https://github.com/JuliaLang/julia/pull/44776. See the [docs](https://docs.julialang.org/en/v1.9-dev/base/base/#Base.@assume_effects) for `@assume_effects`. Can also use `Base.@infer_effects` to see if it’s needed (https://github.com/JuliaLang/julia/pull/44785).