[RFC] Support the latest versions of GHC

[friedbrice]

This is a tentative PR. I'd like to merge it, but I'm not adamant. This PR eliminates almost all CPP, closing https://github.com/scotty-web/scotty/issues/252. (Some CPP is kept around for gating certain tests by platform support.)

So, I'd like to tackle some of the Issues, such as https://github.com/scotty-web/scotty/issues/262, https://github.com/scotty-web/scotty/issues/258, and https://github.com/scotty-web/scotty/issues/272, and I would need to smooth out and simplify project maintenance before doing so.

I'd like to hear what thoughts @scotty-web/admins, @fumieval, @RyanGlScott, and other interested parties have about the following changes.

• remove most CPP
• use Cabal 3.0
• add ghc 9.2, 9.4 to ci
• drop ghc pre 8.10 from ci
• move library files to src/
• fourmolu and hlint
• make copyright in license files agree with copyright in cabal files

[fumieval]

It might be too late, but it would be nice to separate code style changes at least

[friedbrice]

@fumieval good call. i can easily split them out :-)

[ocramz]

good call. i can easily split them out :-)

Hi @friedbrice , would you be able to move this forward so we do one last review and merge? Thank you!

[ocramz]

Let's have separate PRs for linting and functional changes in the future.