feat(joystick/vector): Update to return const ref where possible (#416)

* feat(joystick/vector): Update to return `const ref` where possible
* Update `espp::Vector2d` and `espp::Joystick` to return const references where possible

Reduces the amount of unnecessary copies in application code

Build and run `math/example` and `joystick/example`

* add missing const ref to vector

* Update components/joystick/include/joystick.hpp

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* fix comments

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: finger563

components/joystick/include/joystick.hpp

@@ -202,8 +202,9 @@ class Joystick : public BaseComponent {
   /**
    * @brief Get the most recently updated calibrated position.
    * @return The most recent position (from when update() was last called).
+   * @note The returned reference is valid as long as the Joystick object is alive.
    */
-  espp::Vector2f position() const;
+  const espp::Vector2f &position() const;
 
   /**
    * @brief Get the most recently updated raw / uncalibrated readings. This
@@ -212,8 +213,9 @@ class Joystick : public BaseComponent {
    *        structures.
    * @return The most recent raw measurements (from when update() was last
    *         called).
+   * @note The returned reference is valid as long as the Joystick object is alive.
    */
-  espp::Vector2f raw() const;
+  const espp::Vector2f &raw() const;
 
   friend struct fmt::formatter<Joystick>;
 

components/joystick/src/joystick.cpp

@@ -74,9 +74,9 @@ float espp::Joystick::x() const { return position_.x(); }
 
 float espp::Joystick::y() const { return position_.y(); }
 
-espp::Vector2f espp::Joystick::position() const { return position_; }
+const espp::Vector2f &espp::Joystick::position() const { return position_; }
 
-espp::Vector2f espp::Joystick::raw() const { return raw_; }
+const espp::Vector2f &espp::Joystick::raw() const { return raw_; }
 
 void espp::Joystick::recalculate(float raw_x, float raw_y) {
   raw_.x(raw_x);

components/math/include/vector2d.hpp

@@ -76,7 +76,7 @@ template <typename T> class Vector2d {
    * @brief Getter for the x value.
    * @return The current x value.
    */
-  T x() const { return x_; }
+  const T &x() const { return x_; }
 
   /**
    * @brief Setter for the x value.
@@ -88,7 +88,7 @@ template <typename T> class Vector2d {
    * @brief Getter for the y value.
    * @return The current y value.
    */
-  T y() const { return y_; }
+  const T &y() const { return y_; }
 
   /**
    * @brief Setter for the y value.