refactor camera and mandelbulb to separate modules

src/camera.rs

@@ -0,0 +1,12 @@
+use bevy::prelude::*;
+
+pub fn plugin(app: &mut App) {
+    app.add_systems(Startup, setup);
+}
+
+fn setup(mut commands: Commands) {
+    commands.spawn((
+        Camera3d::default(),
+        Transform::from_xyz(-2.0, 2.5, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
+    ));
+}