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/lib.rs

@@ -13,7 +13,9 @@ pub mod scoring;
 // when decoding instructions to piles in `instruction_to_piles`) and do not
 // appear in any public method signature.
 pub use card_game::{Card, Deck, Rank, Session, SolveError, Suit};
-pub use klondike::{DrawStockConfig, Foundation, Klondike, KlondikeInstruction, KlondikePile, Tableau};
+pub use klondike::{
+    DrawStockConfig, Foundation, Klondike, KlondikeInstruction, KlondikePile, Tableau,
+};
 
 // Solvability check API (delegates to `card_game::Session::solve`); replaces the
 // former `solitaire_data::solver` wrapper module.