QuickCheck Imp integration

[lehins]

Description

Changes in this PR allows us to write QuickCheck properties with ImpSpec:

We can either use Arbitrary (however only for a single argument, which can be a nested tuple):

  it "test1" $ \(foo, blah) -> do
    kh <- freshKeyHash
    show kh `shouldBe` foo
    blah `shouldBe` foo

or manually running an ImpTestM somewhere inside a regular hspec/quickcheck property

  it "test2" $ \impState ->
    forAll arbitrary $ \foo ->
      forAll arbitrary $ \blah ->
        evalImpTestM impState $ do
          kh <- freshKeyHash
          show kh `shouldBe` foo
          blah `shouldBe` foo

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated
• 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)
• 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)
• 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)
• Self-reviewed the diff

[Soupstraw]

Nice!