Add JavaDoc comments to Rotation interface

Added JavaDoc descriptions for the `pitch()` and `yaw()` methods, as well as the interface itself. This improves code readability and provides clear documentation for developers.

paper-api/src/main/java/io/papermc/paper/math/Rotation.java

@@ -2,9 +2,22 @@
 
 import org.jspecify.annotations.NullMarked;
 
+/**
+ * Represents a rotation with specified pitch and yaw values.
+ */
 @NullMarked
 public interface Rotation {
+    /**
+     * Retrieves the pitch component of the rotation, measured in degrees.
+     *
+     * @return the pitch value in degrees
+     */
     float pitch();
 
+    /**
+     * Retrieves the yaw component of the rotation, measured in degrees.
+     *
+     * @return the yaw value in degrees
+     */
     float yaw();
 }