Nix files.

These new Nix files can be used as an alternative to the Stack-based
build.

Change-Id: I56ae4e27fa26541cd88583a7806f2834cb6a1735
diff --git a/mulkup.cabal b/mulkup.cabal
index e5f5976..82fc1a6 100644
--- a/mulkup.cabal
+++ b/mulkup.cabal
@@ -13,21 +13,22 @@
   --     GHC == 9.0.1
 
   build-depends:
-    , base                   ^>= 4.15.0
-    , relude                 ^>= 1.0.0.0
+    , base
+    , relude
     , aeson
-    , bytestring             ^>= 0.10
-    , co-log                 ^>= 0.4
-    , co-log-core            ^>= 0.2.1
-    , co-log-polysemy        ^>= 0.0.1
-    , dhall                  ^>= 1.39
-    , optparse-applicative    >= 0.15     && < 0.17
-    , optics                 ^>= 0.4
-    , polysemy                >= 1.3       && < 1.7
-    , recursion-schemes      ^>= 5.2
+    , bytestring
+    , co-log
+    , co-log-core
+    , co-log-polysemy
+    , containers
+    , dhall
+    , optparse-applicative
+    , optics
+    , polysemy
+    , recursion-schemes
     , time
-    , text                   ^>= 1.2
-    , turtle                 ^>= 1.5.20
+    , text
+    , turtle
 
   default-extensions:
       BangPatterns
@@ -126,8 +127,8 @@
       Mulkup.ConfigSpec
 
   build-depends:
-    , base                   ^>= 4.15.0
-    , tasty                  ^>= 1.4
-    , tasty-hunit            ^>= 0.10
-    , tasty-smallcheck       ^>= 0.8
+    , base
+    , tasty
+    , tasty-hunit
+    , tasty-smallcheck
     , mulkup