share some code between bitvec and native

src/bitboard.rs

@@ -64,11 +64,6 @@ impl BitBoard {
         self.0 |= 1 << index
     }
 
-    #[cfg(not(feature = "bitvec"))]
-    pub const fn count(&self) -> usize {
-        self.0.count_ones() as usize
-    }
-
     const fn get_index(row: usize, col: usize) -> usize {
         row * BOARD_SIZE + col
     }
@@ -83,9 +78,9 @@ impl BitBoard {
         self.0.set(Self::get_index(row, col), value);
     }
 
-    #[cfg(feature = "bitvec")]
+    // works on both `bitvec` and native
     pub fn count(&self) -> usize {
-        self.0.count_ones()
+        self.0.count_ones() as usize
     }
 }