Add Snell's Law refraction algorithm (#7150)

* Add Snell's Law implementation for refraction angle

* Add tests for Snell's Law calculations

* Update documentation with reference link to Snell's Law

Added a reference link to Snell's Law in the documentation.

* Prevent instantiation of SnellLaw class

Make SnellLaw class non-instantiable by adding a private constructor.

* Rename SnellsLawTest to SnellLawTest

* Refactor SnellLawTest for clarity and accuracy

* Rename SnellsLaw.java to SnellLaw.java

* Refactor SnellLawTest with additional assertions

* Refactor SnellLaw class constructor and error handling

Refactor SnellLaw constructor and error message formatting.

* Fix missing newline at end of SnellLawTest.java

Ensure that the SnellLawTest class has a newline at the end of the file.

* Simplify assertions in SnellLawTest

* Simplify exception throwing for total internal reflection

src/test/java/com/thealgorithms/physics/SnellLawTest.java

@@ -0,0 +1,41 @@
+package com.thealgorithms.physics;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Test;
+
+public class SnellLawTest {
+
+    @Test
+    public void testRefractedAngle() {
+        double n1 = 1.0; // air
+        double n2 = 1.5; // glass
+        double theta1 = Math.toRadians(30);
+
+        double theta2 = SnellLaw.refractedAngle(n1, n2, theta1);
+
+        double expected = Math.asin(n1 / n2 * Math.sin(theta1));
+
+        assertEquals(expected, theta2, 1e-12);
+    }
+
+    @Test
+    public void testTotalInternalReflection() {
+        double n1 = 1.5;
+        double n2 = 1.0;
+        double theta1 = Math.toRadians(60); // large angle
+
+        assertThrows(IllegalArgumentException.class, () -> SnellLaw.refractedAngle(n1, n2, theta1));
+    }
+
+    @Test
+    public void testNoTotalInternalReflectionAtLowAngles() {
+        double n1 = 1.5;
+        double n2 = 1.0;
+        double theta1 = Math.toRadians(10);
+
+        assertDoesNotThrow(() -> SnellLaw.refractedAngle(n1, n2, theta1));
+    }
+}