Benchmarks

Hey,

I see you made `eff` compile with GHC 9.6 on a branch, so I re-enabled `eff` benchmarks in `effectful` [here](https://github.com/haskell-effectful/effectful/tree/bench-eff).

You can see how it currently fares against other libraries by running `cabal run bench -- -p countdown.1000` and `cabal run bench -- -p filesize.1000`.