feat(physics): add runtime physics scaffolding

tests/Physics/test_physics_world.cpp

@@ -0,0 +1,37 @@
+#include <gtest/gtest.h>
+
+#include <XCEngine/Physics/PhysicsWorld.h>
+#include <XCEngine/Scene/Scene.h>
+
+namespace {
+
+TEST(PhysicsWorld_Test, DefaultWorldStartsUninitialized) {
+    XCEngine::Physics::PhysicsWorld world;
+
+    EXPECT_FALSE(world.IsInitialized());
+}
+
+TEST(PhysicsWorld_Test, InitializeStoresCreateInfoWithoutMarkingWorldReadyYet) {
+    XCEngine::Components::Scene scene("PhysicsScene");
+    XCEngine::Physics::PhysicsWorld world;
+    XCEngine::Physics::PhysicsWorldCreateInfo createInfo;
+    createInfo.scene = &scene;
+    createInfo.gravity = XCEngine::Math::Vector3(0.0f, -3.5f, 0.0f);
+
+    const bool expectedInitialized = XCEngine::Physics::PhysicsWorld::IsPhysXAvailable();
+
+    EXPECT_EQ(world.Initialize(createInfo), expectedInitialized);
+    EXPECT_EQ(world.IsInitialized(), expectedInitialized);
+    EXPECT_EQ(world.GetCreateInfo().scene, &scene);
+    EXPECT_EQ(world.GetCreateInfo().gravity, XCEngine::Math::Vector3(0.0f, -3.5f, 0.0f));
+}
+
+TEST(PhysicsWorld_Test, StepWithoutInitializationIsNoOp) {
+    XCEngine::Physics::PhysicsWorld world;
+
+    world.Step(0.016f);
+
+    EXPECT_FALSE(world.IsInitialized());
+}
+
+} // namespace