Silence useless clippy warnings

Those warnings are either explicitly accounted for in the code, or make
the code look worse if fixed.

src/board/castle_rights.rs

@@ -67,6 +67,7 @@ impl CastleRights {
     }
 
     /// Add some [CastleRights], and return the resulting [CastleRights].
+    #[allow(clippy::should_implement_trait)]
     #[inline(always)]
     pub fn add(self, to_remove: CastleRights) -> Self {
         // SAFETY: we know the value is in-bounds

src/board/chess_board.rs

@@ -190,6 +190,7 @@ impl ChessBoard {
     fn is_valid(&self) -> bool {
         // Don't overlap pieces.
         for piece in Piece::iter() {
+            #[allow(clippy::collapsible_if)]
             for other in Piece::iter() {
                 if piece != other {
                     if !(self.piece_occupancy(piece) & self.piece_occupancy(other)).is_empty() {

src/board/move.rs

@@ -84,6 +84,7 @@ mod shift {
 
 impl Move {
     /// Construct a new move.
+    #[allow(clippy::too_many_arguments)]
     #[inline(always)]
     fn new(
         piece: Piece,