[BitBoard] Clean up the API; implement some traits

Clean up the BitBoard API by renaming methods with simpler names.
run-help Redo
Redo the implementation of a couple methods to be more succinct.

bitboard/src/bitboard.rs

@@ -25,7 +25,7 @@ impl BitBoard {
 
     #[must_use]
     pub const fn empty() -> BitBoard {
-        BitBoard(0)
+        Self::EMPTY
     }
 
     #[must_use]
@@ -79,8 +79,8 @@ impl BitBoard {
 
 impl BitBoard {
     #[must_use]
-    pub const fn as_bits(&self) -> &u64 {
-        &self.0
+    pub const fn as_bits(&self) -> u64 {
+        self.0
     }
 
     /// Returns `true` if the [`BitBoard`] has no bits set.
@@ -113,7 +113,7 @@ impl BitBoard {
     }
 
     /// Returns `true` if this [`BitBoard`] has the bit corresponding to `square` set.
-    pub fn is_set(self, square: Square) -> bool {
+    pub fn contains(self, square: Square) -> bool {
         let square_bitboard: BitBoard = square.into();
         !(self & square_bitboard).is_empty()
     }
@@ -132,14 +132,14 @@ impl BitBoard {
         self.0.count_ones()
     }
 
-    pub fn set_square(&mut self, sq: Square) {
-        let sq_bb: BitBoard = sq.into();
-        *self |= sq_bb
+    pub fn set(&mut self, square: Square) {
+        let square_bitboard: BitBoard = square.into();
+        self.0 |= square_bitboard.0
     }
 
-    pub fn clear_square(&mut self, sq: Square) {
-        let sq_bb: BitBoard = sq.into();
-        *self &= !sq_bb
+    pub fn clear(&mut self, square: Square) {
+        let square_bitboard: BitBoard = square.into();
+        self.0 &= !square_bitboard.0
     }
 
     /// Returns `true` if this BitBoard represents a single square.
@@ -202,6 +202,12 @@ impl Default for BitBoard {
     }
 }
 
+impl From<BitBoard> for u64 {
+    fn from(value: BitBoard) -> Self {
+        value.as_bits()
+    }
+}
+
 impl From<File> for BitBoard {
     fn from(value: File) -> Self {
         library::FILES[*value.as_index() as usize]
@@ -228,13 +234,10 @@ impl From<Square> for BitBoard {
 
 impl FromIterator<Square> for BitBoard {
     fn from_iter<T: IntoIterator<Item = Square>>(iter: T) -> Self {
-        let mut builder = BitBoardBuilder::empty();
-
-        for sq in iter {
-            builder = builder.square(sq)
-        }
-
-        builder.build()
+        iter.into_iter().fold(BitBoard::EMPTY, |mut acc, sq| {
+            acc.set(sq);
+            acc
+        })
     }
 }