Add Temperature Conversion Utility (#7066)

- Implements conversions between Celsius, Fahrenheit, and Kelvin
- Includes all 6 conversion methods
- Adds comprehensive unit tests with edge cases
- Fixes #6936

Author: krishna-medapati

src/main/java/com/thealgorithms/conversions/TemperatureConverter.java

@@ -0,0 +1,46 @@
+package com.thealgorithms.conversions;
+
+/**
+ * A utility class to convert between different temperature units.
+ *
+ * <p>This class supports conversions between the following units:
+ * <ul>
+ *   <li>Celsius</li>
+ *   <li>Fahrenheit</li>
+ *   <li>Kelvin</li>
+ * </ul>
+ *
+ * <p>This class is final and cannot be instantiated.
+ *
+ * @author krishna-medapati (https://github.com/krishna-medapati)
+ * @see <a href="https://en.wikipedia.org/wiki/Conversion_of_scales_of_temperature">Wikipedia: Temperature Conversion</a>
+ */
+public final class TemperatureConverter {
+
+    private TemperatureConverter() {
+    }
+
+    public static double celsiusToFahrenheit(double celsius) {
+        return celsius * 9.0 / 5.0 + 32.0;
+    }
+
+    public static double celsiusToKelvin(double celsius) {
+        return celsius + 273.15;
+    }
+
+    public static double fahrenheitToCelsius(double fahrenheit) {
+        return (fahrenheit - 32.0) * 5.0 / 9.0;
+    }
+
+    public static double fahrenheitToKelvin(double fahrenheit) {
+        return (fahrenheit - 32.0) * 5.0 / 9.0 + 273.15;
+    }
+
+    public static double kelvinToCelsius(double kelvin) {
+        return kelvin - 273.15;
+    }
+
+    public static double kelvinToFahrenheit(double kelvin) {
+        return (kelvin - 273.15) * 9.0 / 5.0 + 32.0;
+    }
+}

src/test/java/com/thealgorithms/conversions/TemperatureConverterTest.java

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+package com.thealgorithms.conversions;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+class TemperatureConverterTest {
+
+    private static final double DELTA = 0.01;
+
+    @Test
+    void testCelsiusToFahrenheit() {
+        assertEquals(32.0, TemperatureConverter.celsiusToFahrenheit(0.0), DELTA);
+        assertEquals(212.0, TemperatureConverter.celsiusToFahrenheit(100.0), DELTA);
+        assertEquals(-40.0, TemperatureConverter.celsiusToFahrenheit(-40.0), DELTA);
+        assertEquals(98.6, TemperatureConverter.celsiusToFahrenheit(37.0), DELTA);
+    }
+
+    @Test
+    void testCelsiusToKelvin() {
+        assertEquals(273.15, TemperatureConverter.celsiusToKelvin(0.0), DELTA);
+        assertEquals(373.15, TemperatureConverter.celsiusToKelvin(100.0), DELTA);
+        assertEquals(233.15, TemperatureConverter.celsiusToKelvin(-40.0), DELTA);
+    }
+
+    @Test
+    void testFahrenheitToCelsius() {
+        assertEquals(0.0, TemperatureConverter.fahrenheitToCelsius(32.0), DELTA);
+        assertEquals(100.0, TemperatureConverter.fahrenheitToCelsius(212.0), DELTA);
+        assertEquals(-40.0, TemperatureConverter.fahrenheitToCelsius(-40.0), DELTA);
+        assertEquals(37.0, TemperatureConverter.fahrenheitToCelsius(98.6), DELTA);
+    }
+
+    @Test
+    void testFahrenheitToKelvin() {
+        assertEquals(273.15, TemperatureConverter.fahrenheitToKelvin(32.0), DELTA);
+        assertEquals(373.15, TemperatureConverter.fahrenheitToKelvin(212.0), DELTA);
+        assertEquals(233.15, TemperatureConverter.fahrenheitToKelvin(-40.0), DELTA);
+    }
+
+    @Test
+    void testKelvinToCelsius() {
+        assertEquals(0.0, TemperatureConverter.kelvinToCelsius(273.15), DELTA);
+        assertEquals(100.0, TemperatureConverter.kelvinToCelsius(373.15), DELTA);
+        assertEquals(-273.15, TemperatureConverter.kelvinToCelsius(0.0), DELTA);
+    }
+
+    @Test
+    void testKelvinToFahrenheit() {
+        assertEquals(32.0, TemperatureConverter.kelvinToFahrenheit(273.15), DELTA);
+        assertEquals(212.0, TemperatureConverter.kelvinToFahrenheit(373.15), DELTA);
+        assertEquals(-40.0, TemperatureConverter.kelvinToFahrenheit(233.15), DELTA);
+    }
+}