refactor fish prepare for polymorphism

src/Entity.h

@@ -5,15 +5,20 @@
 #include <unordered_map>
 #include <vector>
 
+struct AssetPair {
+  std::vector<std::string> image;
+  std::vector<std::string> mask;
+};
+
 class Entity {
 protected:
   float x;
   float y;
 
 public:
-  Entity() : x(0), y(0) {}
-  virtual ~Entity() {}
+  Entity() : x(0.0f), y(0.0f) {}
+  virtual ~Entity() = default;
 
-  inline float getX() const { return x; }
-  inline float getY() const { return y; }
+  float getX() const noexcept { return x; }
+  float getY() const noexcept { return y; }
 };