Fix incompatibility with GHC 9.6

[FPtje]

Follow-up of GHC 9.6. It looks like the dependencies for GHC 9.6 now work, so that makes this a good opportunity to fix UUAGC(-cabal) as well.

Short summary of changes:

• Replace ErrorT with ExceptT. ErrorT has been deprecated for a while, and ErrorT has existed since 2014 (added in transformers-0.4.0.0). I would have used some CPP pragma to keep it backwards compatible, but AG files don't seem to like those.
• Import some monad functions from Control.Monad. I think some of them were removed from Prelude, causing the error. Importing them from Control.Monad should be fine for backwards compatibility.
• Replace fail for the ST s monad with its original implementation. See Remove MonadFail (ST s) instance(s) haskell/core-libraries-committee#33, the MonadFail instance of ST s was removed. Its original implementation was considered to be against the spirit of MonadFail.

Tested by running cabal build from GHC 9.6, 9.4, 9.2 and 9.0.

[jbransen]

This looks good, thank you!