Cleanup imports and extensions

[arcz]

This uses the new ImportQualifiedPost extensions that allows more natural placement of qualified keyword. I cleaned up the imports alphabetically, dividing them into common, hevm, and echidna as we tend to style this and made this consistent throughout the codebase.

We also use a lot of extensions that will become standard starting from GHC 9.2 - https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/control.html#extension-GHC2021. I removed those from the sources and placed them as default extensions. When we update to 9.2 we can simply remove them from package.yaml.

EDIT: I had to update hlint action as it was too old and didn't recognize ImportQualifiedPost