feat(xanthous): Fistfighting builds knuckle calluses

2000 ticks after the character damages their fists by hitting something,
the character now develops calluses on their fists (scaled by *how*
damaged they've become) that reduce the chance of them receiving
additional damage from hitting things - up to a max of 5, which
prevents *all* damage from fistfighting.

This is all tracked in a new "Knuckles" struct in a new "Body" struct on
the character datatype, which manages stepping itself forward as part of
the Brain impl on the character.

Change-Id: Ica269f16fb340fb25900d2c77fbad32f10c00be2
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3222
Reviewed-by: grfn <grfn@gws.fyi>
Tested-by: BuildkiteCI

users/grfn/xanthous/test/Xanthous/Entities/CharacterSpec.hs

@@ -0,0 +1,24 @@
+{-# OPTIONS_GHC -Wno-type-defaults #-}
+--------------------------------------------------------------------------------
+module Xanthous.Entities.CharacterSpec (main, test) where
+--------------------------------------------------------------------------------
+import           Test.Prelude
+--------------------------------------------------------------------------------
+import           Xanthous.Entities.Character
+import           Xanthous.Util (endoTimes)
+--------------------------------------------------------------------------------
+
+main :: IO ()
+main = defaultMain test
+
+test :: TestTree
+test = testGroup "Xanthous.Entities.CharacterSpec"
+  [ testGroup "Knuckles"
+    [ testBatch $ monoid @Knuckles mempty
+    , testGroup "damageKnuckles"
+      [ testCase "caps at 5" $
+          let knuckles' = endoTimes 6 damageKnuckles mempty
+          in _knuckleDamage knuckles' @?= 5
+      ]
+    ]
+  ]