[board] Replace PieceSet's derived Hash and PartialEq with bespoke implementation

The piece set duplicates some data to make lookups more efficient. Only use the
necessary, unique data for these functions.

board/src/piece_sets.rs

@@ -5,7 +5,10 @@ mod mailbox;
 use self::mailbox::Mailbox;
 use chessfriend_bitboard::{BitBoard, IterationDirection};
 use chessfriend_core::{Color, Piece, Shape, Square};
-use std::ops::BitOr;
+use std::{
+    hash::{Hash, Hasher},
+    ops::BitOr,
+};
 use thiserror::Error;
 
 #[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
@@ -21,9 +24,9 @@ pub enum PlacePieceError {
     ExisitingPiece { piece: Piece, square: Square },
 }
 
-/// The internal data structure of a [Board] that efficiently manages the
+/// The internal data structure of a [`Board`] that efficiently manages the
 /// placement of pieces on the board.
-#[derive(Clone, Debug, Default, Eq, Hash, PartialEq)]
+#[derive(Clone, Debug, Default, Eq)]
 pub struct PieceSet {
     mailbox: Mailbox,
     color_occupancy: [BitBoard; Color::NUM],
@@ -140,6 +143,20 @@ impl PieceSet {
     }
 }
 
+impl Hash for PieceSet {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.color_occupancy.hash(state);
+        self.shape_occupancy.hash(state);
+    }
+}
+
+impl PartialEq for PieceSet {
+    fn eq(&self, other: &Self) -> bool {
+        self.color_occupancy == other.color_occupancy
+            && self.shape_occupancy == other.shape_occupancy
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;