add: async wrapper for pp calculate

src/osu/pp.rs

@@ -261,6 +261,11 @@ impl<'m> OsuPP<'m> {
         unreachable!()
     }
 
+    #[inline]
+    pub async fn calculate_async(self) -> PpResult {
+        self.calculate()
+    }
+
     /// Returns an object which contains the pp and [`DifficultyAttributes`](crate::osu::DifficultyAttributes)
     /// containing stars and other attributes.
     ///