Implements struggle.

pkmn_lib_interface/src/app_interface/dynamic_data/pokemon.rs

@@ -291,6 +291,8 @@ pub enum DamageSource {
     MoveDamage = 0,
     /// The damage is done by something else.
     Misc = 1,
+    /// The damage is done because of struggling.
+    Struggle = 2,
 }
 
 crate::handling::cacheable::cacheable!(Pokemon);