Add benchmark button to UI

The benchmark button is only enabled in release builds. If clicked, it
will trigger the benchmark suite.

src/main.rs

@@ -397,6 +397,18 @@ impl eframe::App for CompilerApp {
                 {
                     self.run_all_tests();
                 }
+
+                ui.separator();
+
+                let is_debug = cfg!(debug_assertions);
+                ui.add_enabled_ui(!is_debug, |ui| {
+                    let bench_btn = ui.button("⏱ Bench");
+                    if is_debug {
+                        bench_btn.on_hover_text("Benchmarks are only available in Release builds.");
+                    } else if bench_btn.clicked() {
+                        self.run_benchmarks(false);
+                    }
+                });
             });
             ui.add_space(2.0);
         });