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_engine/src/schedule_checks.rs

@@ -90,9 +90,7 @@ mod tests {
                     .and_then(|prefix| prefix.split_whitespace().last())
                     .and_then(|n| n.parse::<usize>().ok());
                 parsed.unwrap_or_else(|| {
-                    panic!(
-                        "ambiguity panic message no longer parseable (Bevy upgrade?): {msg}"
-                    )
+                    panic!("ambiguity panic message no longer parseable (Bevy upgrade?): {msg}")
                 })
             }
         };