CHALLENGE 2: Horizontal Movement With get_axis()
====================================================================

TASK
----
Create move_left/move_right actions and write a script using
Input.get_axis() that moves a Sprite2D horizontally at 250 pixels
per second in whichever direction is held, with no movement when
neither is pressed.

SETUP
-----
1. Project > Project Settings > Input Map.
2. Add a "move_left" action, bind it to the left arrow (or A).
3. Add a "move_right" action, bind it to the right arrow (or D).

SOLUTION CODE (attached to the Sprite2D)
--------------------------------------------
extends Sprite2D

const SPEED = 250.0

func _physics_process(delta: float) -> void:
    var horizontal := Input.get_axis("move_left", "move_right")
    position.x += horizontal * SPEED * delta

WHY THIS WORKS AS AN ANSWER
----------------------------
Input.get_axis("move_left", "move_right") returns a single float:
-1.0 while move_left is held, 1.0 while move_right is held, and 0.0
whenever neither (or both, cancelling out) is pressed. Multiplying
that value by SPEED * delta gives the exact frame-rate-independent
movement amount to add to position.x this frame - when the result is
0.0, position.x doesn't change at all, satisfying the "no movement
when neither is pressed" part of the task automatically, with no
separate if/else needed to handle that case.

This is the same delta-scaled movement pattern used since Chapter 1
and Chapter 4 - the only new part here is that the direction (1, -1,
or 0) now comes from real keyboard input each frame instead of being
a fixed constant.