board backing referencing improvements

src/repr/bitboard.rs

@@ -5,7 +5,6 @@ use super::{
 };
 use static_assertions::const_assert;
 
-#[cfg(not(feature = "bitvec"))]
 pub type BitBoardInner = u64;
 
 #[derive(Copy, Clone, PartialEq, Eq)]
@@ -42,6 +41,10 @@ impl BitBoard {
         self.0.count_ones() as usize
     }
 
+    pub const fn is_empty(&self) -> bool {
+        self.0 == 0
+    }
+
     // Directional shifts with edge masking (prevents wrapping)
     pub const fn east(&self) -> Self {
         let mask = !Self::col_mask(Board::BOARD_SIZE - 1).0; // Mask to block column 7 bits