Convert generated levels to walls

Add support for converting generated levels to walls, and merge one into
the entity map at the beginning of the game.

There's nothing here that guarantees the character ends up *inside* the
level though (they almost always don't) so that'll have to be slotted
into the level generation process.

test/Xanthous/Generators/UtilSpec.hs

@@ -41,7 +41,7 @@ test = testGroup "Xanthous.Generators.Util"
                 $ randInitialize dims aliveChance
         in bounds res === ((0, 0), (dims ^. width, dims ^. height))
     ]
-  , testGroup "numAliveNeighbors"
+  , testGroup "numAliveNeighborsM"
     [ testProperty "maxes out at 8" $ \(GenArray (arr :: Array (Word, Word) Bool)) loc ->
         let
           act :: forall s. ST s Word
@@ -51,6 +51,17 @@ test = testGroup "Xanthous.Generators.Util"
           res = runST act
         in counterexample (show res) $ between 0 8 res
     ]
+  , testGroup "numAliveNeighbors"
+    [ testProperty "is equivalient to runST . numAliveNeighborsM . thaw" $
+      \(GenArray (arr :: Array (Word, Word) Bool)) loc ->
+        let
+          act :: forall s. ST s Word
+          act = do
+            mArr <- thaw @_ @_ @_ @(STUArray s) arr
+            numAliveNeighborsM mArr loc
+          res = runST act
+        in numAliveNeighbors arr loc === res
+    ]
   , testGroup "cloneMArray"
       [ testCase "clones the array" $ runST $
           let