Use GHCi's full support for multiple home units, from GHC 9.14.1

[mpilgrem]

stack ghci (and stack repl) loads up GHCi with all the library and executable components of all the packages in the Stack project. However, there are limitations. GHCi's full support for multiple home units from GHC 9.14.1 may allow those limitations to be overcome.

See:

• https://www.well-typed.com/blog/2025/06/ghci-multiple-home-units/
• https://discourse.haskell.org/t/well-typed-blog-making-ghci-compatible-with-multiple-home-units/12328