Extract biology processing from AltStyle into Pet

I'm trying to pull more of the modeling code out of the individual
classes, and into this encapsulated preprocessing, so it's a lot more
in-one-place!

app/models/alt_style.rb

@@ -74,15 +74,6 @@ class AltStyle < ApplicationRecord
     Item.appearances_for(items, self, ...)
   end
 
-  def biology=(biology)
-    # TODO: This is very similar to what `PetState` does, but like… much much
-    # more compact? Idk if I'm missing something, or if I was just that much
-    # more clueless back when I wrote it, lol 😅
-    self.swf_assets = biology.values.map do |asset_data|
-      SwfAsset.from_biology_data(self.body_id, asset_data)
-    end
-  end
-
   # At time of writing, most batches of Alt Styles thumbnails used a simple
   # pattern for the item thumbnail URL, but that's not always the case anymore.
   # For now, let's keep using this format as the default value when creating a

app/models/pet.rb

@@ -110,9 +110,7 @@ class Pet < ApplicationRecord
     def alt_style
       @alt_style ||= begin
         return nil unless @custom_pet[:alt_style]
-
         raise UnexpectedDataFormat unless @custom_pet[:alt_color]
-        raise UnexpectedDataFormat if @custom_pet[:biology_by_zone].empty?
 
         id = @custom_pet[:alt_style].to_i
         AltStyle.find_or_initialize_by(id:).tap do |alt_style|
@@ -120,7 +118,7 @@ class Pet < ApplicationRecord
             color_id: @custom_pet[:alt_color].to_i,
             species_id: @custom_pet[:species_id].to_i,
             body_id: @custom_pet[:body_id].to_i,
-            biology: @custom_pet[:biology_by_zone],
+            swf_assets: alt_style_assets,
           )
         end
       end
@@ -139,12 +137,20 @@ class Pet < ApplicationRecord
         biology = @custom_pet[:alt_style].present? ?
           @custom_pet[:original_biology] :
           @custom_pet[:biology_by_zone]
-        raise UnexpectedDataFormat if biology.empty?
+        assets_from_biology(biology)
+      end
+    end
 
+    def alt_style_assets
+      raise UnexpectedDataFormat if @custom_pet[:biology_by_zone].empty?
+      assets_from_biology(@custom_pet[:biology_by_zone])
+    end
+
+    def assets_from_biology(biology)
+      raise UnexpectedDataFormat if biology.empty?
       body_id = @custom_pet[:body_id].to_i
       biology.values.map { |b| SwfAsset.from_biology_data(body_id, b) }
     end
   end
-  end
 end