[moves] Add several macros to help with testing: ply! and assert_move_list!

ply! implements a small DSL for writing moves in code using a natural-ish
algebraic notation.

assert_move_list! takes a generator and an expected list of moves and asserts
that they're equal. This macro is mostly a copy from one I wrote earlier in the
position crate.

moves/src/generators.rs

@@ -2,6 +2,9 @@
 
 mod pawn;
 
+#[cfg(test)]
+mod testing;
+
 pub use pawn::PawnMoveGenerator;
 
 use crate::Move;
@@ -11,6 +14,12 @@ pub struct GeneratedMove {
     pub(crate) ply: Move,
 }
 
+impl std::fmt::Display for GeneratedMove {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.ply.fmt(f)
+    }
+}
+
 impl From<Move> for GeneratedMove {
     fn from(value: Move) -> Self {
         GeneratedMove { ply: value }