Fix CMake cannot find 'oxidd_ffi' target

[SSoelvsten]

With 70d6d82 , the 'oxidd-ffi' target was treated as if renamed to 'oxidd_ffi' even though 'corrosion_import_crate' still creates said target with the previous name.

[nhusung]

The solution is a different one: As discussed in corrosion-rs/corrosion#501, target names will change in Rust 1.79 to not have dashes but underscores. On its own, the respective change in OxiDD does not break anything as long as you use oxidd in CMake (and not oxidd-ffi, or now oxidd_ffi) to refer to the library. The problem in BDD Benchmark is that we also use lib-bdd-ffi, which also depends on Corrosion but used v4.x while I recently updated to Corrosion v5.0 here. Somehow, different Corrosion versions interfere with each other. Yesterday, I also updated lib-bdd-ffi to Corrosion v5.0, so now it works again. Just merge SSoelvsten/bdd-benchmark#121 to update the libraries :)

[SSoelvsten]

Thanks!