(NonEmpty x) in MemberSpec

[TimSheard]

MemberSpec used to have type
MemberSpec :: [a] -> Specification fn a

This was problematic because (MemberSpec [ ]) is inconsistent and cannot be solved, Yet it carries no information about the context that held when this inconsistency arose. This lead to many baffling failures.

By changing the type of MemberSpec to
MemberSpec :: (Data.List.NonEmpty a) -> Specification fn a
We use types to enforce this baffing inconsistency never arises.
Contexts that used to compute (MemberSpec [ ]) can now instead compute (ErrorSpec (context about error)) instead

Checklist

• [ x] Commit sequence broadly makes sense and commits have useful messages
• [x ] New tests are added if needed and existing tests are updated
• All visible changes are prepended to the latest section of a CHANGELOG.md for the affected packages.
  New section is never added with the code changes. (See RELEASING.md)
• When applicable, versions are updated in .cabal and CHANGELOG.md files according to the
  versioning process.
• The version bounds in .cabal files for all affected packages are updated.
  If you change the bounds in a cabal file, that package itself must have a version increase. (See RELEASING.md)
• Code is formatted with fourmolu (use scripts/fourmolize.sh)
• Cabal files are formatted (use scripts/cabal-format.sh)
• hie.yaml has been updated (use scripts/gen-hie.sh)
• [ x] Self-reviewed the diff