Parallelize DFS, use an AtomicBool for short-circuiting

time:   [73.407 µs 76.145 µs 79.345 µs]
change: [−40.126% −24.679% −3.8062%] (p = 0.04 < 0.05)

src-tauri/benches/rayon.rs

@@ -0,0 +1,53 @@
+use std::hint::black_box;
+
+use criterion::{criterion_group, criterion_main, Criterion};
+use rota_lib::{
+    config::{ToxicPair, UserConfig},
+    resident::Resident,
+    schedule::{MonthlySchedule, ShiftType},
+    scheduler::Scheduler,
+    slot::Day,
+    workload::WorkloadTracker,
+};
+
+fn criterion_benchmark(c: &mut Criterion) {
+    let config = maximal_config();
+    let scheduler = Scheduler::new_with_config(config);
+
+    c.bench_function("scheduler run", |b| {
+        b.iter(|| {
+            let mut schedule = MonthlySchedule::new();
+            let mut tracker = WorkloadTracker::default();
+            let result = scheduler.run(&mut schedule, &mut tracker);
+            black_box(result)
+        })
+    });
+}
+
+fn maximal_config() -> UserConfig {
+    UserConfig::default()
+        .with_holidays(vec![2, 3, 10, 11, 12, 25])
+        .with_residents(vec![
+            Resident::new(1, "R1").with_max_shifts(3),
+            Resident::new(2, "R2").with_max_shifts(4),
+            Resident::new(3, "R3").with_reduced_load(),
+            Resident::new(4, "R4").with_allowed_types(vec![ShiftType::Closed]),
+            Resident::new(5, "R5")
+                .with_allowed_types(vec![ShiftType::OpenFirst, ShiftType::OpenSecond]),
+            Resident::new(6, "R6").with_negative_shifts(vec![Day(5), Day(15), Day(25)]),
+            Resident::new(7, "R7")
+                .with_allowed_types(vec![ShiftType::OpenFirst, ShiftType::OpenSecond]),
+            Resident::new(8, "R8"),
+            Resident::new(9, "R9"),
+            Resident::new(10, "R10").with_reduced_load(),
+        ])
+        .with_toxic_pairs(vec![
+            ToxicPair::new(1, 2),
+            ToxicPair::new(3, 4),
+            ToxicPair::new(3, 5),
+            ToxicPair::new(7, 8),
+        ])
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);