Disable GameCube adapter on Windows (#80)

## Summary
- add a feature flag for the GameCube adapter driver
- keep the driver enabled by default on supported platforms
- exclude the adapter dependency and polling systems on Windows

Reviewed-on: #80
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/input/gamecube/mod.rs

@@ -1,10 +1,23 @@
+#[cfg(all(feature = "gamecube-adapter", not(target_os = "windows")))]
 pub mod bridge;
+#[cfg(all(feature = "gamecube-adapter", not(target_os = "windows")))]
 pub mod poll;
 
-pub use bridge::{GC_PORT_COUNT, GcPort, GcPorts};
+#[cfg(all(feature = "gamecube-adapter", not(target_os = "windows")))]
+pub use bridge::{GC_PORT_COUNT, GcPort};
+#[cfg(all(feature = "gamecube-adapter", not(target_os = "windows")))]
 pub use poll::{GcAdapterSnapshot, GcPortState};
 
+#[derive(Resource, Default)]
+pub struct GcPorts {
+    pub entities: [Option<Entity>; 4],
+    #[cfg(all(feature = "gamecube-adapter", not(target_os = "windows")))]
+    pub(super) last: [poll::GcPortState; 4],
+}
+
+#[cfg(all(feature = "gamecube-adapter", not(target_os = "windows")))]
 use bevy::input::InputSystems;
+#[cfg(all(feature = "gamecube-adapter", not(target_os = "windows")))]
 use bevy::input::gamepad::{gamepad_connection_system, gamepad_event_processing_system};
 use bevy::prelude::*;
 
@@ -15,21 +28,24 @@ impl Plugin for GamecubeAdapterPlugin {
     fn build(&self, app: &mut App) {
         app.init_resource::<GcPorts>();
 
-        let Ok(snapshot) = poll::spawn_poll_thread() else {
-            // No adapter connected; leave GcPorts empty and skip wiring the
-            // polling systems.
-            return;
-        };
+        #[cfg(all(feature = "gamecube-adapter", not(target_os = "windows")))]
+        {
+            let Ok(snapshot) = poll::spawn_poll_thread() else {
+                // No adapter connected; leave GcPorts empty and skip wiring the
+                // polling systems.
+                return;
+            };
 
-        app.insert_resource(snapshot).add_systems(
-            PreUpdate,
-            (
-                bridge::gc_connection_system.before(gamepad_connection_system),
-                bridge::gc_event_system
-                    .after(gamepad_connection_system)
-                    .before(gamepad_event_processing_system),
-            )
-                .in_set(InputSystems),
-        );
+            app.insert_resource(snapshot).add_systems(
+                PreUpdate,
+                (
+                    bridge::gc_connection_system.before(gamepad_connection_system),
+                    bridge::gc_event_system
+                        .after(gamepad_connection_system)
+                        .before(gamepad_event_processing_system),
+                )
+                    .in_set(InputSystems),
+            );
+        }
     }
 }