[position] Implement generating pawn moves by looking up bitboards in the Library

This enables a bunch of clean up! Remove the MoveGenerationParameters and MoveList
types from move_generator::pawn.

Implement BitBoard::pawn_pushes to look up pawn pushes by square and color.

bitboard/src/bitboard.rs

@@ -44,6 +44,10 @@ impl BitBoard {
         library().pawn_attacks(sq, color)
     }
 
+    pub fn pawn_pushes(sq: Square, color: Color) -> BitBoard {
+        library().pawn_pushes(sq, color)
+    }
+
     moves_getter!(knight_moves);
     moves_getter!(bishop_moves);
     moves_getter!(rook_moves);

bitboard/src/library.rs

@@ -58,6 +58,7 @@ pub(super) struct MoveLibrary {
 
     // Piecewise move tables
     pawn_attacks: [[BitBoard; 64]; 2],
+    pawn_pushes: [[BitBoard; 64]; 2],
     knight_moves: [BitBoard; 64],
     bishop_moves: [BitBoard; 64],
     rook_moves: [BitBoard; 64],
@@ -70,6 +71,7 @@ impl MoveLibrary {
         MoveLibrary {
             rays: [[BitBoard::empty(); 8]; Square::NUM],
             pawn_attacks: [[BitBoard::empty(); 64]; 2],
+            pawn_pushes: [[BitBoard::empty(); 64]; 2],
             knight_moves: [BitBoard::empty(); 64],
             bishop_moves: [BitBoard::empty(); 64],
             rook_moves: [BitBoard::empty(); 64],
@@ -169,10 +171,29 @@ impl MoveLibrary {
 
     fn init_pawn_moves(&mut self, sq: Square) {
         let bitboard: BitBoard = sq.into();
+
         self.pawn_attacks[Color::White as usize][sq as usize] =
             bitboard.shift_north_west_one() | bitboard.shift_north_east_one();
         self.pawn_attacks[Color::Black as usize][sq as usize] =
             bitboard.shift_south_west_one() | bitboard.shift_south_east_one();
+
+        self.pawn_pushes[Color::White as usize][sq as usize] = {
+            let mut push = bitboard.shift_north_one();
+            if !(bitboard & RANKS[1]).is_empty() {
+                push |= push.shift_north_one();
+            }
+
+            push
+        };
+
+        self.pawn_pushes[Color::Black as usize][sq as usize] = {
+            let mut push = bitboard.shift_south_one();
+            if !(bitboard & RANKS[6]).is_empty() {
+                push |= push.shift_south_one();
+            }
+
+            push
+        };
     }
 
     #[inline]
@@ -192,6 +213,10 @@ impl MoveLibrary {
         self.rays[sq as usize][dir as usize]
     }
 
+    pub(super) fn pawn_pushes(&self, sq: Square, color: Color) -> BitBoard {
+        self.pawn_pushes[color as usize][sq as usize]
+    }
+
     pub(super) fn pawn_attacks(&self, sq: Square, color: Color) -> BitBoard {
         self.pawn_attacks[color as usize][sq as usize]
     }