FFI for Pokemon Party, make Pokemon Party use interior mutability.

src/dynamic_data/models/battle_party.rs

@@ -45,7 +45,7 @@ impl BattleParty {
     }
 
     /// Gets a Pokemon at an index.
-    pub fn get_pokemon(&self, index: usize) -> &Option<Arc<Pokemon>> {
+    pub fn get_pokemon(&self, index: usize) -> Option<Arc<Pokemon>> {
         self.party.at(index)
     }