Rework the source so that battle is in its own thing to work on.

meson.build

@@ -84,6 +84,7 @@ sources = [
   'animation.cpp',
   'animation.cpp',
   'autowalker.cpp',
+  'battle.cpp',
   'boss_fight_ui.cpp',
   'camera.cpp',
   'combat.cpp',
@@ -126,7 +127,9 @@ sources = [
 
 executable('runtests', sources + [
   'tests/ai.cpp',
+  'tests/animation.cpp',
   'tests/base.cpp',
+  'tests/battle.cpp',
   'tests/components.cpp',
   'tests/config.cpp',
   'tests/dbc.cpp',
@@ -142,10 +145,8 @@ executable('runtests', sources + [
   'tests/matrix.cpp',
   'tests/pathing.cpp',
   'tests/rituals.cpp',
-  'tests/combat.cpp',
   'tests/sound.cpp',
   'tests/spatialmap.cpp',
-  'tests/animation.cpp',
   'tests/stats.cpp',
   'tests/textures.cpp',
   'tests/tilemap.cpp',