style: cargo fmt under rustfmt 1.9 and gate formatting in CI

The repo was formatted under an older stable; rustfmt 1.9 (Rust 1.95)
wraps signatures and call sites differently, so every touched file was
picking up unrelated formatting hunks. One mechanical pass, and a
'cargo fmt --check' step in the test workflow (same pinned 1.95.0
toolchain) so drift can't accumulate again.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

solitaire_core/src/proptest_tests.rs

@@ -41,13 +41,20 @@ fn all_cards(game: &GameState) -> Vec<Card> {
         );
     }
     for t in &tableaux {
-        cards.extend(game.pile(KlondikePile::Tableau(*t)).iter().map(|(c, _)| c.clone()));
+        cards.extend(
+            game.pile(KlondikePile::Tableau(*t))
+                .iter()
+                .map(|(c, _)| c.clone()),
+        );
     }
     cards
 }
 
 fn draw_mode_strategy() -> impl Strategy<Value = DrawStockConfig> {
-    prop_oneof![Just(DrawStockConfig::DrawOne), Just(DrawStockConfig::DrawThree)]
+    prop_oneof![
+        Just(DrawStockConfig::DrawOne),
+        Just(DrawStockConfig::DrawThree)
+    ]
 }
 
 /// Apply a sequence of random actions to a game, silently ignoring errors.